fix: add auth endpoints to server, fix auth bypass and registration

- server/: commit server code for the first time (was untracked)
  - POST /auth/signup and /auth/login endpoints now deployed
  - GET /v1/billing/summary now verifies user exists in auth_users
    (prevents stale JWTs from bypassing auth → fixes empty dashboard)
- app/_layout.tsx: dual-marker install check (SQLite + SecureStore)
  to detect fresh installs reliably on Android
- app/auth/login.tsx, signup.tsx: replace Ionicons leaf logo with
  actual app icon image (assets/icon.png)
- services/authService.ts: log HTTP status + server message on auth errors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/app.json

@@ -0,0 +1,9 @@
+{
+  "expo": {
+    "extra": {
+      "eas": {
+        "projectId": "4fb7372e-83ce-4f18-9b48-e735f00d7243"
+      }
+    }
+  }
+}