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>

.gitignore

@@ -11,6 +11,9 @@ node_modules
 dist
 dist-ssr
 *.local
+server/.env
+server/data/*.sqlite
+server/data/*.sqlite-*
 
 # Editor directories and files
 .vscode/*
@@ -22,3 +25,10 @@ dist-ssr
 *.njsproj
 *.sln
 *.sw?
+
+# Expo
+.expo/
+
+# Claude / Agents (symlinks incompatible with EAS Build on Windows)
+.agents/
+.claude/