fix(webhook): remove comment-based approve, keep status-only verdict

Status-only verdict model: comments NEVER drive the pipeline. Removed the
whole comment-based control mechanism from handle_comment (:approved: /
:rejected: / answer-to-questions) which caused bug 3 (echo self-hit): the
analyst posts its own "waiting for approval" comment, handle_comment catches
its own comment and reverts In Review -> In Progress. handle_comment is now a
pure logger with no side effects.

handle_status_start: a return to In Progress on an EXISTING task (Slava
answered the analyst questions in Needs Input) now RELAUNCHES the stage agent
instead of being a no-op. Distinguished from a duplicate In Progress webhook
via has_active_job_for_task() (new db helper): no active job => agent idle =>
relaunch; active job => busy => skip (no double launch).

src/db.py

@@ -351,6 +351,23 @@ def mark_job(
     conn.close()
 
 
+def has_active_job_for_task(task_id: int) -> bool:
+    """True if the task already has a queued or running job.
+
+    Used by the status-only verdict model (handle_status_start) to guard against
+    double-launching an agent when a duplicate In Progress webhook arrives or a
+    job is still in flight. The events de-dup absorbs identical webhook bodies;
+    this guards against distinct webhooks while a job is pending/running.
+    """
+    conn = get_db()
+    row = conn.execute(
+        "SELECT 1 FROM jobs WHERE task_id = ? AND status IN ('queued','running') LIMIT 1",
+        (task_id,),
+    ).fetchone()
+    conn.close()
+    return row is not None
+
+
 def count_running_jobs() -> int:
     """Number of jobs currently in 'running' status (for max_concurrency)."""
     conn = get_db()