feat!: backend-only architecture, remove frontend/nginx (v1.2.0)

- Remove frontend/ and nginx/ from core (each customer owns their frontend)
- Update docker-compose.yml to backend-only (postgres + redis + backend)
- Update docker-compose.prod.yml to backend-only
- Add CLAUDE.md with dev guidelines
- Update README.md with new architecture diagram

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/tsconfig.app.json

@@ -1,28 +0,0 @@
-{
-  "compilerOptions": {
-    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.app.tsbuildinfo",
-    "target": "ES2023",
-    "useDefineForClassFields": true,
-    "lib": ["ES2023", "DOM", "DOM.Iterable"],
-    "module": "ESNext",
-    "types": ["vite/client"],
-    "skipLibCheck": true,
-
-    /* Bundler mode */
-    "moduleResolution": "bundler",
-    "allowImportingTsExtensions": true,
-    "verbatimModuleSyntax": true,
-    "moduleDetection": "force",
-    "noEmit": true,
-    "jsx": "react-jsx",
-
-    /* Linting */
-    "strict": true,
-    "noUnusedLocals": true,
-    "noUnusedParameters": true,
-    "erasableSyntaxOnly": true,
-    "noFallthroughCasesInSwitch": true,
-    "noUncheckedSideEffectImports": true
-  },
-  "include": ["src"]
-}