feat(hindsight): richer session-scoped retain metadata

- Add configurable retain_tags / retain_source / retain_user_prefix /
  retain_assistant_prefix knobs for native Hindsight.
- Thread gateway session identity (user_name, chat_id, chat_name,
  chat_type, thread_id) through AIAgent and MemoryManager into
  MemoryProvider.initialize kwargs so providers can scope and tag
  retained memories.
- Hindsight attaches the new identity fields as retain metadata,
  merges per-call tool tags with configured default tags, and uses
  the configurable transcript labels for auto-retained turns.

Co-authored-by: Abner <abner.the.foreman@agentmail.to>

gateway/run.py

@@ -6475,6 +6475,11 @@ class GatewayRunner:
                     session_id=task_id,
                     platform=platform_key,
                     user_id=source.user_id,
+                    user_name=source.user_name,
+                    chat_id=source.chat_id,
+                    chat_name=source.chat_name,
+                    chat_type=source.chat_type,
+                    thread_id=source.thread_id,
                     session_db=self._session_db,
                     fallback_model=self._fallback_model,
                 )
@@ -9718,6 +9723,11 @@ class GatewayRunner:
                     session_id=session_id,
                     platform=platform_key,
                     user_id=source.user_id,
+                    user_name=source.user_name,
+                    chat_id=source.chat_id,
+                    chat_name=source.chat_name,
+                    chat_type=source.chat_type,
+                    thread_id=source.thread_id,
                     gateway_session_key=session_key,
                     session_db=self._session_db,
                     fallback_model=self._fallback_model,