fix(observability): merge-gate on deploy, full token input, Plane Done, artifact links

1. BUG 8 (second door): merge webhook no longer fake-completes a task at the
   deploy stage; done is gated by the deployer verdict (check_deploy_status).
   Other stages keep merge->done.
2. Token accounting: parse+persist cache_creation_input_tokens (new
   idempotent agent_runs column). usage_comment / task_summary now show the
   FULL input (input + cache_read + cache_creation) with a cached breakdown.
   cost_usd untouched.
3. deploy->done success now forces the Plane issue to terminal Done state.
4. All agents (architect/developer/reviewer/tester/deployer) attach artifact
   links to their finish comment via gitea_public_url.

Tests added for each fix; pytest 244 passed / 9 failed (off-limits HMAC group).

src/webhooks/gitea.py

@@ -334,6 +334,20 @@ async def handle_pr(payload: dict):
                 logger.error(f"Task {task_id}: max retries reached, needs manual intervention")
 
     elif action == "closed" and pr.get("merged", False):
+        # BUG 8 (second door): at the deploy stage `done` is gated by the
+        # deployer's verdict (check_deploy_status via advance_stage), NOT by the
+        # fact that the PR was merged. The deployer merges the PR at the START of
+        # its run, so a merged webhook arrives ~30s later while the deployer is
+        # still working — blindly setting done here would fake-complete the task
+        # and discard a later deploy_status: FAILED verdict. advance_stage will
+        # drive deploy→done (and Plane→Done) when the deployer job finishes.
+        # For every OTHER stage the merge-driven done behaviour is preserved.
+        if current_stage == "deploy":
+            logger.info(
+                f"Task {task_id}: PR merged at deploy stage — done gated by "
+                f"deployer verdict (check_deploy_status), ignoring merge-driven done."
+            )
+            return
         update_task_stage(task_id, "done")
         notify_stage_change(task_id, current_stage, "done")
         logger.info(f"Task {task_id}: PR merged, stage → done")