feat: remote browser login persistence + balance display + UI consistency

- Retain login state in remote browser profiles (don't delete on disconnect)
- Add GET /api/browser-sessions/{id}/clipboard for clipboard sync
- Add POST /api/browser-sessions/{id}/autofill-login for manual credential fill
- Add DELETE /api/browser-sessions/profiles/{custom_page_id} for login clear
- Add balance tracking with configurable divisor (balance_divisor)
- Health check on session reuse, idle TTL eviction, background cleanup
- Add first-frame watchdog (10s timeout) to prevent infinite loading
- Reconnect browser on active=true when session was closed
- UI: uniform text-only inline buttons (websites + upstreams pages)
- Fix page switch race with closingRemoteSessionPromise

.gitignore

@@ -21,3 +21,7 @@ backend/data/
 *.log
 .DS_Store
 .git-real/
+
+# 外部项目（不提交）
+/sub2api/
+/new-api/