refactor(runtime): restructure runs module with new execution architecture

Major refactoring of deerflow/runtime/:
- runs/callbacks/ - new callback system (builder, events, title, tokens)
- runs/internal/ - execution internals (executor, supervisor, stream_logic, registry)
- runs/internal/execution/ - execution artifacts and events handling
- runs/facade.py - high-level run facade
- runs/observer.py - run observation protocol
- runs/types.py - type definitions
- runs/store/ - simplified store interfaces (create, delete, query, event)

Refactor stream_bridge/:
- Replace old providers with contract.py and exceptions.py
- Remove async_provider.py, base.py, memory.py

Add documentation:
- README.md and README_zh.md for runtime module

Remove deprecated:
- manager.py moved to internal/
- worker.py, schemas.py
- user_context.py

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/packages/harness/deerflow/runtime/runs/callbacks/title.py

@@ -0,0 +1,51 @@
+"""Title capture callback for runs."""
+
+from __future__ import annotations
+
+from typing import Any
+from uuid import UUID
+
+from langchain_core.callbacks import BaseCallbackHandler
+
+
+class RunTitleCallback(BaseCallbackHandler):
+    """Capture title generated by title middleware LLM calls or custom events."""
+
+    def __init__(self) -> None:
+        super().__init__()
+        self._title: str | None = None
+
+    def on_llm_end(self, response: Any, *, run_id: UUID, **kwargs: Any) -> None:
+        if self._identify_caller(kwargs) != "middleware:title":
+            return
+        try:
+            message = response.generations[0][0].message
+        except (IndexError, AttributeError):
+            return
+        content = getattr(message, "content", "")
+        if isinstance(content, str) and content:
+            self._title = content.strip().strip('"').strip("'")[:200]
+
+    def on_custom_event(self, name: str, data: Any, *, run_id: UUID, **kwargs: Any) -> None:
+        if name not in {"title", "thread_title", "middleware:title"}:
+            return
+        if isinstance(data, str):
+            self._title = data.strip()[:200]
+            return
+        if isinstance(data, dict):
+            title = data.get("title")
+            if isinstance(title, str):
+                self._title = title.strip()[:200]
+
+    def title(self) -> str | None:
+        return self._title
+
+    def _identify_caller(self, kwargs: dict[str, Any]) -> str:
+        for tag in kwargs.get("tags") or []:
+            if isinstance(tag, str) and (
+                tag.startswith("subagent:")
+                or tag.startswith("middleware:")
+                or tag == "lead_agent"
+            ):
+                return tag
+        return "lead_agent"