Add backlog audit and task update command

- agents/prompts/backlog_audit.md: QA analyst prompt for checking
  which pending tasks are already implemented in the codebase
- agents/runner.py: run_audit() — project-level agent that reads
  all pending tasks, inspects code, returns classification
- cli/main.py: kin audit <project_id> — runs audit, offers to mark
  done tasks; kin task update <id> --status --priority
- web/api.py: POST /api/projects/{id}/audit (runs audit inline),
  POST /api/projects/{id}/audit/apply (batch mark as done)
- Frontend: "Audit backlog" button on ProjectView with results
  modal showing already_done/still_pending/unclear categories

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

web/api.py

@@ -385,6 +385,47 @@ def list_tickets(project: str | None = None, status: str | None = None):
     return tickets
 
 
+# ---------------------------------------------------------------------------
+# Audit
+# ---------------------------------------------------------------------------
+
+@app.post("/api/projects/{project_id}/audit")
+def audit_project(project_id: str):
+    """Run backlog audit — check which pending tasks are already done."""
+    from agents.runner import run_audit
+
+    conn = get_conn()
+    p = models.get_project(conn, project_id)
+    if not p:
+        conn.close()
+        raise HTTPException(404, f"Project '{project_id}' not found")
+    result = run_audit(conn, project_id, noninteractive=True)
+    conn.close()
+    return result
+
+
+class AuditApply(BaseModel):
+    task_ids: list[str]
+
+
+@app.post("/api/projects/{project_id}/audit/apply")
+def audit_apply(project_id: str, body: AuditApply):
+    """Mark tasks as done after audit confirmation."""
+    conn = get_conn()
+    p = models.get_project(conn, project_id)
+    if not p:
+        conn.close()
+        raise HTTPException(404, f"Project '{project_id}' not found")
+    updated = []
+    for tid in body.task_ids:
+        t = models.get_task(conn, tid)
+        if t and t["project_id"] == project_id:
+            models.update_task(conn, tid, status="done")
+            updated.append(tid)
+    conn.close()
+    return {"updated": updated, "count": len(updated)}
+
+
 # ---------------------------------------------------------------------------
 # Bootstrap
 # ---------------------------------------------------------------------------