Add .dockerignore so BuildKit ignores host node_modules

.dockerignore

@@ -0,0 +1,53 @@
+# Patterns excluded from the Docker build context.
+#
+# Distinct from .openenvignore: that one filters the openenv-push upload
+# to the HF Space repo. THIS file filters what `docker build` (and HF's
+# BuildKit) actually sees when running COPY directives.
+#
+# Both are needed because:
+#   1. .openenvignore keeps junk out of the Hub repo (browsable in UI).
+#   2. .dockerignore keeps the SAME junk out of the BuildKit context
+#      even when shipped — without this, an earlier failed deploy left
+#      `frontend/node_modules` on the Space's git, and `COPY frontend/`
+#      collided with the freshly-installed in-image node_modules:
+#        ERROR: cannot copy to non-directory:
+#               /.../buildkit/.../build/node_modules/@types/katex
+#
+#   The fix: never let host node_modules into the build context, period.
+
+# Frontend dev artefacts. Stage 1 of the Dockerfile reinstalls node_modules
+# from package.json + pnpm-lock.yaml; whatever the host has should not
+# leak into the COPY frontend/ step that runs after pnpm install.
+frontend/node_modules
+frontend/dist
+frontend/dist-ts-build
+
+# Python venv / caches. These are huge and useless inside the image.
+.venv
+**/__pycache__
+**/*.pyc
+**/*.pyo
+.pytest_cache
+.ruff_cache
+.mypy_cache
+
+# Training stack. Built into a separate HF Job image; not needed at
+# Space runtime.
+train
+
+# Tests + dev docs. Keep the build context focused on runtime code.
+tests
+docs
+
+# Build / packaging artefacts.
+*.egg-info
+build
+dist
+
+# IDE / OS detritus.
+.DS_Store
+*.swp
+.vscode
+.idea
+.git
+.github