Rewrite run_local_agent: code-based flow, concurrency guard, remove isApproved

- Replace LLM-driven triage with code-based directory scan and project fetch
- Two-step LLM approach: Step 1 classifies file→project+domains, Step 2 processes with tools
- Add domain descriptions to Step 1 prompt for better extraction accuracy
- Add _running_agents set for per-agent concurrency guard (one running instance per agent)
- Return 409 from route before DB write when agent already running
- Remove is_approved from task_agent create/update tools and system prompt
- Remove is_approved from timeline_agent create/update tools and system prompt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/agents/task_agent.py

@@ -29,7 +29,7 @@ TASK_SYSTEM_PROMPT = (
     "  - project_id is optional; link to a project when the user mentions one\n"
     "  - is_ai_suggested: 1 only when proactively proposing a task the user\n"
     "    did not explicitly request; 0 otherwise\n"
-    "  - is_approved defaults to 0; set to 1 only when the user confirms\n"
+    "  - is_ai_suggested: 1 only when proactively proposing a task the user did not explicitly request; 0 otherwise\n"
     "  - Use list_tasks_due_today for 'what's due today' queries\n"
     "  - For update_task, use -1 for integer fields you do not want to change\n"
     "  - Always confirm the action in plain, user-friendly language."
@@ -79,7 +79,6 @@ async def create_task(
     due_date: int = 0,
     project_id: str = "",
     is_ai_suggested: int = 0,
-    is_approved: int = 0,
 ) -> str:
     """Create a new task.
     title: task title (required)
@@ -90,7 +89,6 @@ async def create_task(
     due_date: Unix timestamp in milliseconds; 0 means no due date
     project_id: optional UUID of the parent project
     is_ai_suggested: 1 if proactively suggested, 0 if user-requested
-    is_approved: 0 until the user confirms; 1 when confirmed
     """
     result = await execute_on_client(
         action="insert",
@@ -104,7 +102,6 @@ async def create_task(
             "dueDate": due_date or None,
             "projectId": project_id or None,
             "isAiSuggested": is_ai_suggested,
-            "isApproved": is_approved,
         },
     )
     row = result["row"]
@@ -124,12 +121,10 @@ async def update_task(
     assignees: str = "",
     due_date: int = -1,
     project_id: str = "",
-    is_approved: int = -1,
 ) -> str:
     """Update fields on an existing task. Only pass fields you want to change.
     task_id: the task's UUID (required)
     due_date: -1 means unchanged; 0 clears the due date; any positive value sets it
-    is_approved: -1 means unchanged; 0 or 1 sets the value
     """
     updates: dict[str, Any] = {}
     if title:
@@ -146,8 +141,6 @@ async def update_task(
         updates["dueDate"] = due_date or None
     if project_id:
         updates["projectId"] = project_id
-    if is_approved != -1:
-        updates["isApproved"] = is_approved
     result = await execute_on_client(
         action="update",
         table="tasks",