chore: bump to v0.9.19-rc.1 and add local OpenAPI build support

- Add release candidate (rc) support to release.sh with latestRC tagging
- Bump VERSION, backend pyproject.toml, and frontend package.json to 0.9.19-rc.1
- Add local frontend/openapi.json so build no longer needs running backend
- Update generate:types and validate-types.sh to use local openapi.json
- Fix frontend tests: remove unused imports/variables and update mock data

frontend/package.json

@@ -1,12 +1,12 @@
 {
   "name": "bangui-frontend",
   "private": true,
-  "version": "0.9.19",
+  "version": "0.9.19-rc.1",
   "description": "BanGUI frontend — fail2ban web management interface",
   "type": "module",
   "scripts": {
     "dev": "vite",
-    "generate:types": "openapi-typescript http://localhost:8000/api/openapi.json -o src/types/generated.ts",
+    "generate:types": "openapi-typescript ./openapi.json -o src/types/generated.ts",
     "validate:types": "bash scripts/validate-types.sh",
     "build": "npm run generate:types && tsc --noEmit && vite build",
     "preview": "vite preview",