feat: production release with React SPA, file attachments, and deploy tooling

Backend:
- Add file_handlers.go: presigned upload/download for item attachments
- Add item_files.go: item file and thumbnail DB operations
- Add migration 011: item_files table and thumbnail_key column
- Update items/projects/relationships DB with extended field support
- Update routes: React SPA serving from web/dist, file upload endpoints
- Update auth handlers and middleware for cookie + bearer token auth
- Remove Go HTML templates (replaced by React SPA)
- Update storage client for presigned URL generation

Frontend:
- Add TagInput component for tag/keyword entry
- Add SVG assets for Silo branding and UI icons
- Update API client and types for file uploads, auth, extended fields
- Update AuthContext for session-based auth flow
- Update LoginPage, ProjectsPage, SchemasPage, SettingsPage
- Fix tsconfig.node.json

Deployment:
- Update config.prod.yaml: single-binary SPA layout at /opt/silo
- Update silod.service: ReadOnlyPaths for /opt/silo
- Add scripts/deploy.sh: build, package, ship, migrate, start
- Update docker-compose.yaml and Dockerfile
- Add frontend-spec.md design document

.gitignore

@@ -38,7 +38,9 @@ __pycache__/
 *.egg-info/
 .eggs/
 dist/
-build/
+# Python build output (not build/package/ which holds our Dockerfile)
+/build/*
+!/build/package/
 
 # FreeCAD
 *.FCStd1
@@ -47,3 +49,6 @@ build/
 # Web frontend
 web/node_modules/
 web/dist/
+web/*.tsbuildinfo
+web/vite.config.d.ts
+web/vite.config.js