Stop tracking workspace/; bundled-demos/ is the canonical demo source

`workspace/` is runtime state (per-user folders, no-auth dev's `code/`)
and shouldn't be in git. The same files were previously committed under
both `workspace/code/` and `src/static/bundled-demos/`, which forced a
Docker `diff -q` sync check and leaked user-scoped paths into version
control.

- /workspace/ added to .gitignore; all previously tracked files removed
  via `git rm --cached`.
- src/static/bundled-demos/ becomes the single source of truth: panel16
  demos, led_tutorial, led_patterns, neopixel demos, and main.py move
  here alongside the existing canonical demos.
- New BUNDLED_DEMOS_DIR config; user_workspace seeders read from it.
- main.py lifespan seeds WORKSPACE_ROOT/code/ on startup so a fresh
  clone running `pipenv run dev` still gets the full sample set
  (existing files never overwritten — user edits survive restarts).
- Dockerfile drops `COPY workspace` and the diff sanity check.
- README/LED_TUTORIAL repointed at the new canonical paths.
- test_led_patterns loads led_patterns.py from bundled-demos.
- test_api uses mkdir(exist_ok=True) for `code/` (startup pre-creates).

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

@@ -14,17 +14,8 @@ RUN pipenv install --system --deploy
 COPY src ./src
 COPY lib ./lib
 RUN mkdir -p src/static/bundled-lib && cp -f lib/*.py src/static/bundled-lib/
-COPY workspace ./workspace
-# Sanity-check: the canonical demos under `src/static/bundled-demos/` (used by
-# the editor's "Reset demos" button) must stay in sync with `workspace/code/`.
-# Files in `bundled-demos/` are committed to git and copied via `COPY src`
-# above; this step just fails the build if a checked-in copy drifted from the
-# canonical version, so the mismatch is caught here instead of at runtime.
-RUN for f in pattern_rainbow_demo.py pattern_twinkle_demo.py pattern_chase_demo.py \
-             adc_slider_demo.py pin_demo.py serial_demo.py; do \
-        diff -q "workspace/code/$f" "src/static/bundled-demos/$f" \
-            || { echo "ERROR: $f out of sync between workspace/code/ and src/static/bundled-demos/" >&2; exit 1; }; \
-    done
+# `workspace/` is runtime/user state (gitignored) and is created on demand
+# at app startup — the image does not need to ship it.
 
 EXPOSE 8080