feat(core): add shared structured logger with idempotent handler attach

chore: lock Python to 3.10–3.12 to match cp312-capped wheel availability

chore: pin runtime + dev dependencies for all three modalities

docs: tighten AGENTS.md — clarify Data Readiness checklist and storage boundary

docs: add AGENTS.md with vision, layout, standards, data readiness rules

chore: track planning docs and ignore .sixth/ tooling dir

chore: bootstrap NeuroBridge project skeleton