feat: add version management with setuptools-scm

- Configure hatch-vcs for automatic version generation from git tags
- Update pyproject.toml to use dynamic versioning
- Add src/_version.py for runtime version access
- Update src/__init__.py to import version from _version
- Add __APP_VERSION__ to frontend vite config
- Add version script to frontend package.json
- Update CI workflows to trigger on version tags instead of branches

frontend/package.json

@@ -12,7 +12,8 @@
     "test:ui": "vitest --ui",
     "test:run": "vitest run",
     "lint": "eslint . --fix",
-    "type-check": "vue-tsc --noEmit"
+    "type-check": "vue-tsc --noEmit",
+    "version": "git describe --tags --always"
   },
   "dependencies": {
     "@types/dompurify": "^3.0.5",