Add Docker image, compose, and Gitea CI

- Multi-stage Dockerfile builds server + web into a single node:20-alpine
  image; runtime serves API on /api and the SPA from /app/public.
- Express now serves web/dist with an SPA fallback that skips /api so API
  misses still 404 cleanly.
- docker-compose.yml is a single-service deploy with a named volume for
  the SQLite database at /data/apothecary.db.
- .gitea/workflows/build.yml pushes :latest, :<sha>, and :semver tags to
  the Gitea container registry on main and v* tags.

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

.dockerignore

@@ -0,0 +1,20 @@
+.git
+.gitignore
+.gitea
+.claude
+.dockerignore
+Dockerfile
+docker-compose.yml
+node_modules
+**/node_modules
+server/dist
+server/data.db
+server/data.db-journal
+server/data.db-shm
+server/data.db-wal
+web/dist
+web/tsconfig.tsbuildinfo
+weed-tracker
+*.log
+.env
+.env.local