Add CalVer build-time version tracking

- Dockerfile: ARG BUILD_VERSION=dev → ENV APP_VERSION baked into image
- ci.yml: BUILD_VERSION passed as build-arg; set to git tag name on v*
  tag builds, "dev" on branch builds
- routes/api.py: GET /api/version returns {"version": APP_VERSION}
- SettingsView: fetches /api/version on mount, displays in About section
  under General tab

Version source of truth is the git tag (YY.MM.DD.N CalVer).
pyproject.toml / package.json versions are no longer maintained.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -21,5 +21,10 @@ COPY alembic/ alembic/
 # Ensure Python finds the source tree (where static files live) before site-packages
 ENV PYTHONPATH=/app/src
 
+# Version is injected at build time via --build-arg BUILD_VERSION=YY.MM.DD.N
+# Falls back to "dev" for local / untagged builds
+ARG BUILD_VERSION=dev
+ENV APP_VERSION=$BUILD_VERSION
+
 EXPOSE 5000
 CMD ["sh", "-c", "alembic upgrade head && hypercorn 'fabledassistant.app:create_app()' --bind 0.0.0.0:5000 --keep-alive 600"]