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/services/upstream_client.py

@@ -34,10 +34,18 @@ def _clean_auth_header_value(value: Any, field_name: str) -> str:
         return ""
     if text.startswith("Bearer "):
         text = text[7:].strip()
+    # Try to sanitize non-latin-1 characters instead of hard-failing
     try:
         text.encode("latin-1")
-    except UnicodeEncodeError as exc:
-        raise UpstreamError(f"{field_name} contains non-HTTP-header characters; please re-extract and apply the full credential") from exc
+    except UnicodeEncodeError:
+        # Try stripping non-ASCII characters
+        cleaned = text.encode("ascii", errors="ignore").decode("ascii").strip()
+        if cleaned:
+            return cleaned
+        raise UpstreamError(
+            f"{field_name} 含有非 HTTP 标头字符（如中文或 emoji），"
+            f"请重新登录后再试"
+        ) from None
     return text
 
 
@@ -325,3 +333,30 @@ class UpstreamClient:
 
     def get_group_rates(self, endpoint: str) -> Any:
         return self._request("GET", endpoint)
+
+    def get_balance(self, endpoint: str, response_path: str) -> Optional[float]:
+        """Call the balance endpoint and extract a numeric value using a dot-separated JSON path.
+
+        response_path 示例：
+          "balance"           → resp["balance"]
+          "data.quota"        → resp["data"]["quota"]
+          "data.total_balance" → resp["data"]["total_balance"]
+        """
+        if not endpoint or not response_path:
+            return None
+        resp = self._request("GET", endpoint)
+        if not isinstance(resp, dict):
+            return None
+        parts = response_path.split(".")
+        value: Any = resp
+        for part in parts:
+            if isinstance(value, dict):
+                value = value.get(part)
+            else:
+                return None
+        if value is None:
+            return None
+        try:
+            return float(value)
+        except (ValueError, TypeError):
+            return None