refactor(auth): extract auth into shared package and unify auth flow

- Introduce new @local/auth package with token store, axios helpers, auth client, and AuthPage UI
- Unify login/register into a single AuthPage with mode switching
- Centralize JWT handling via tokenStore and axios interceptors
- Remove direct localStorage token access from blog app
- Replace blog Login/Register views with single auth view
- Update router (View, VIEW_TREE, VIEW_URL) to support unified auth view
- Fix hook usage by lifting useAuth() to top-level and passing via props
- Refactor Blog view navigation to support auth mode routing
- Clean up ArticleProvider to rely on auth state, not tokens
- Align AuthProvider to delegate token management to auth package
- Remove legacy Login/Register components and props
- Normalize API client creation via shared createApiClient
- Improve type safety and state consistency across auth/article flows

auth/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "@local/auth",
+  "version": "0.1.0",
+  "private": true,
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "peerDependencies": {
+    "react": "^18",
+    "react-dom": "^18"
+  }
+}