feat: PKCE auth + CI/CD deploy

- Frontend: PKCE flow (oauth.ts, AuthCallback code exchange, 401 interceptor)
- Backend: token introspection via SuperOAuth (no more JWT secret)
- User model: superOauthId (unified) replaces oauthId+provider
- Cookies httpOnly session + refresh token
- POST /auth/refresh endpoint
- Gitea CI workflow (vps-runner pattern)
- DB_SYNC env var for initial schema creation

frontend/eslint.config.js

@@ -0,0 +1,23 @@
+import js from '@eslint/js'
+import globals from 'globals'
+import reactHooks from 'eslint-plugin-react-hooks'
+import reactRefresh from 'eslint-plugin-react-refresh'
+import tseslint from 'typescript-eslint'
+import { defineConfig, globalIgnores } from 'eslint/config'
+
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      js.configs.recommended,
+      tseslint.configs.recommended,
+      reactHooks.configs.flat.recommended,
+      reactRefresh.configs.vite,
+    ],
+    languageOptions: {
+      ecmaVersion: 2020,
+      globals: globals.browser,
+    },
+  },
+])