refactor(config): eliminate global mutable state, wire DeerFlowContext into runtime

- Freeze all config models (AppConfig + 15 sub-configs) with frozen=True
- Purify from_file() — remove 9 load_*_from_dict() side-effect calls
- Replace mtime/reload/push/pop machinery with single ContextVar + init_app_config()
- Delete 10 sub-module globals and their getters/setters/loaders
- Migrate 50+ consumers from get_*_config() to get_app_config().xxx

- Expand DeerFlowContext: app_config + thread_id + agent_name (frozen dataclass)
- Wire into Gateway runtime (worker.py) and DeerFlowClient via context= parameter
- Remove sandbox_id from runtime.context — flows through ThreadState.sandbox only
- Middleware/tools access runtime.context directly via Runtime[DeerFlowContext] generic
- resolve_context() retained at server entry points for LangGraph Server fallback

backend/packages/harness/deerflow/agents/memory/queue.py

@@ -7,7 +7,7 @@ from dataclasses import dataclass, field
 from datetime import UTC, datetime
 from typing import Any
 
-from deerflow.config.memory_config import get_memory_config
+from deerflow.config.app_config import AppConfig
 
 logger = logging.getLogger(__name__)
 
@@ -56,7 +56,7 @@ class MemoryUpdateQueue:
             correction_detected: Whether recent turns include an explicit correction signal.
             reinforcement_detected: Whether recent turns include a positive reinforcement signal.
         """
-        config = get_memory_config()
+        config = AppConfig.current().memory
         if not config.enabled:
             return
 
@@ -87,7 +87,7 @@ class MemoryUpdateQueue:
 
     def _reset_timer(self) -> None:
         """Reset the debounce timer."""
-        config = get_memory_config()
+        config = AppConfig.current().memory
 
         # Cancel existing timer if any
         if self._timer is not None: