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

backend/app/models/upstream.py

@@ -1,6 +1,6 @@
 from datetime import datetime, timezone
 from typing import Optional
-from sqlalchemy import Integer, String, Boolean, DateTime, Text
+from sqlalchemy import Integer, String, Boolean, DateTime, Text, Float
 from sqlalchemy.orm import mapped_column, Mapped
 from app.database import Base
 
@@ -26,6 +26,12 @@ class Upstream(Base):
     last_checked_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
     last_error: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
     consecutive_failures: Mapped[int] = mapped_column(Integer, default=0)
+    # Balance tracking
+    balance: Mapped[Optional[float]] = mapped_column(Float, nullable=True)
+    balance_updated_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+    balance_endpoint: Mapped[str] = mapped_column(String(256), default="")
+    balance_response_path: Mapped[str] = mapped_column(String(256), default="")
+    balance_divisor: Mapped[float] = mapped_column(Float, default=1.0)
     created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
     updated_at: Mapped[datetime] = mapped_column(
         DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc)