feat: CONTRIBUTING.md + issue templates + OpenGraph meta tags

Sprint 1 community-workflow unlock files:

- CONTRIBUTING.md: how to contribute (no-code: translate/falsify/preset/bug;
code: setup, structure, recipes, languages, formulas, PR process,
code of conduct, what won't be accepted)
- .github/ISSUE_TEMPLATE/:
* bug-report.md
* feature-request.md
* question.md
* translation.md
* config.yml (blank issues disabled, contact links for registry)
- OpenGraph + Twitter Card meta tags in index.html for rich social sharing
(Twitter, LinkedIn, WhatsApp, Discord all get cards now)
- theme-color meta for mobile browser chrome
- expanded title + description + keywords for SEO

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/bug-report.md

@@ -0,0 +1,45 @@
+---
+name: 🐛 Bug report
+about: Something is broken in TAF Agent
+title: '[Bug] '
+labels: bug
+---
+
+## What happened
+
+Brief description.
+
+## Expected behavior
+
+What should have happened?
+
+## Steps to reproduce
+
+1.
+2.
+3.
+
+## Browser / environment
+
+- Browser: __ (Chrome / Edge / Firefox / Safari + version)
+- OS: __ (Windows / macOS / Linux)
+- Mode used: __ (Profile / Compare / Inspector / Ask / Recipe)
+- Model id (if applicable): __
+
+## Console output
+
+Open DevTools (F12 → Console). Paste any errors:
+
+```
+(paste here)
+```
+
+## Screenshots
+
+If visual bug, attach a screenshot.
+
+## Hash (if error during analysis)
+
+Look at the URL (after Share) or the JSON download for the input hash:
+
+`#________`

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false
+contact_links:
+  - name: 📤 Submit a TAF analysis
+    url: https://github.com/karlesmarin/tafagent-registry/issues/new
+    about: Submit your model analysis to the public registry (use the web tool's Submit button for pre-filled form)
+  - name: ❌ Refute a TAF prediction
+    url: https://github.com/karlesmarin/tafagent-registry/issues/new?template=refutation.md
+    about: Empirical measurement contradicts a TAF prediction
+  - name: 📄 Paper questions
+    url: https://github.com/karlesmarin/NeurIPS
+    about: Discussion about the underlying Transformer Thermodynamics paper

.github/ISSUE_TEMPLATE/feature-request.md

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+---
+name: 💡 Feature request
+about: Suggest a new feature for the web tool
+title: '[Feature] '
+labels: enhancement
+---
+
+## What's the problem this solves
+
+Describe the use case in 1-2 sentences.
+
+## Proposed solution
+
+What would the feature look like? Sketch the UI / behaviour.
+
+## Alternatives considered
+
+What other approaches did you think about? Why is this better?
+
+## Effort estimate
+
+Rough estimate (or leave blank if you don't know):
+- [ ] Small (<2h)
+- [ ] Medium (2-8h)
+- [ ] Large (>8h)
+
+## Are you willing to implement it
+
+- [ ] Yes, I'll submit a PR
+- [ ] I can help review/test
+- [ ] Just suggesting; need someone else to build it
+
+## References
+
+Any papers, blog posts, or other tools that do this well.

.github/ISSUE_TEMPLATE/question.md

@@ -0,0 +1,20 @@
+---
+name: ❓ Question
+about: Ask about how something works
+title: '[Question] '
+labels: question
+---
+
+## My question
+
+What are you trying to understand or do?
+
+## What I've tried
+
+What did you check before asking? (paper, README, help modal, etc.)
+
+## Context
+
+- Are you a researcher / engineer / student / hobbyist?
+- What's the underlying goal? (training a model, evaluating one, etc.)
+- Anything that helps frame the question.

.github/ISSUE_TEMPLATE/translation.md

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+---
+name: 🌐 Translation contribution
+about: Add or fix translations for a language
+title: '[i18n] '
+labels: i18n
+---
+
+## Language
+
+Which language? (code + name, e.g. `de` / Deutsch)
+
+## What you're contributing
+
+- [ ] Adding a new language (full translation)
+- [ ] Fixing a bad translation in an existing language
+- [ ] Translating new keys added in a recent release
+
+## Native speaker?
+
+- [ ] Yes, native speaker
+- [ ] Yes, fluent
+- [ ] Helped by a language model (note which one)
+- [ ] Used machine translation (note which service)
+
+## Files touched
+
+- [ ] `js/i18n.js` (translation strings)
+- [ ] `index.html` (data-i18n attributes if adding new ones)
+
+## Anything specific to flag
+
+Cultural notes, terminology choices, untranslatable terms (kept in English),
+etc.

CONTRIBUTING.md

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+# Contributing to TAF Agent
+
+> Thank you for considering contributing. This is an independent research
+> project — every contribution, however small, is genuinely appreciated.
+
+---
+
+## How you can help (no coding required)
+
+### 🌐 Translate
+Add a language to the UI. Edit `js/i18n.js`, copy the `en` block, translate
+each value. Open a PR. ~1-2h.
+
+### 🧪 Falsify a prediction
+Run TAF Agent on a model where you have *real measurements* (NIAH retrieval,
+PPL benchmarks, training cost data). If our verdict disagrees with reality,
+open a [refutation issue in the registry](https://github.com/karlesmarin/tafagent-registry/issues/new?template=refutation.md).
+Refutations are first-class citizens here.
+
+### ➕ Add a model preset
+Open an [issue with the model's config](https://github.com/karlesmarin/tafagent-registry/issues/new?template=new-preset.md).
+We'll bundle popular ones into the next release.
+
+### 🐛 Report bugs
+Use the [bug report template](https://github.com/karlesmarin/tafagent/issues/new?template=bug-report.md).
+Browser console output (F12 → Console) helps a lot.
+
+### 💡 Propose new recipes
+Suggest new TAF analyses in the [registry recipe template](https://github.com/karlesmarin/tafagent-registry/issues/new?template=new-recipe.md).
+The 5 currently shipped (X-1, X-2, X-3, X-5, X-19) are a starting set; the
+paper outlines 20 candidate recipes.
+
+---
+
+## How you can help (with code)
+
+### Local development setup
+
+```bash
+git clone https://github.com/karlesmarin/tafagent
+cd tafagent
+python -m http.server 8000
+# Open http://localhost:8000 in Chrome/Edge/Firefox 113+
+```
+
+No build step, no npm, no transpilation. Edit files, refresh browser.
+
+### Code structure
+
+```
+index.html             ← UI shell
+style.css              ← dark theme + responsive
+js/main.js             ← orchestration (Pyodide + WebLLM + render)
+js/i18n.js             ← translations (EN/ES/FR/ZH)
+python/taf_browser.py  ← TAF formulas + recipes (runs in Pyodide)
+registry-bootstrap/    ← files for the public registry repo
+```
+
+### Adding a new recipe (X-N)
+
+1. Add the function to `python/taf_browser.py`:
+   ```python
+   def run_recipe_xN(theta, T_train, ...):
+       chain = []
+       # ... build chain step by step using existing TAF formulas
+       return _wrap("X-N", "Name", locals(), chain, verdict, reason, mitigation)
+   ```
+2. Register it in the `RECIPES` dict at the bottom of the file.
+3. Add defaults to `getRecipeDefaults()` in `js/main.js`.
+4. Test locally; submit PR.
+
+### Adding a new language
+
+1. In `js/i18n.js`, add to `LANGUAGES` array:
+   ```javascript
+   { code: "de", flag: "🇩🇪", label: "Deutsch" }
+   ```
+2. Copy the `en` block in `TRANSLATIONS`, translate each value.
+3. Add a flag button in `index.html`:
+   ```html
+   <button class="lang-btn" data-lang="de" data-label="Deutsch" title="Deutsch">🇩🇪</button>
+   ```
+4. Test, submit PR.
+
+### Adding a new TAF formula
+
+1. Add the pure-Python function to `python/taf_browser.py`.
+2. Add a translation key for tooltips in `js/i18n.js`.
+3. If it's a closed-form result usable from a recipe, expose via the
+   recipe runner.
+
+---
+
+## Pull request process
+
+1. Fork the repo.
+2. Branch off `main`: `git checkout -b feat/your-thing`.
+3. Make changes, commit with descriptive messages
+   (`feat:` / `fix:` / `docs:` / `refactor:`).
+4. Push to your fork; open PR against `main`.
+5. Describe what changed and why; reference issue if any.
+6. Be patient — this is maintained part-time.
+
+We rebase + squash PRs for a clean history.
+
+---
+
+## Code of conduct
+
+- Be technical, specific, kind. Disagreements are about math, not people.
+- Citations beat opinions. Measurements beat citations.
+- Assume good faith. Most "wrong" PRs are misunderstandings, not bad actors.
+- No commercial advertisements, no third-party trackers, no telemetry.
+
+---
+
+## What we won't accept
+
+- Anything that adds tracking / analytics / telemetry to the user
+- Closed-source dependencies that lock the tool to a vendor
+- Recipes that require API keys for non-academic models
+- Changes that break the offline-after-first-load promise
+- Submissions that violate model licenses (e.g. uploading gated weights)
+
+---
+
+## Maintainer
+
+Carles Marin · [@karlesmarin](https://github.com/karlesmarin) ·
+transformerkmarin@gmail.com (paper-related) ·
+karlesmarin@gmail.com (project-related)
+
+---
+
+## License
+
+Apache-2.0. By contributing you agree your contribution is licensed under
+the same terms.