feat(render-workers): 4 render 워커 heartbeat 배선 + poll_once 카운터

- services/_shared/heartbeat.py (A1) WorkerStats/utc_now_iso/heartbeat_loop 소비
- image-render / video-render / music-render / insta-render 각 worker.py:
  stats = WorkerStats() 모듈 레벨 추가, poll_once에서 dispatch 전 busy=True,
  ack 후 jobs_done+1 / fail 후 jobs_failed+1 + last_job_at + busy=False
- 각 main.py: lifespan에 aioredis(decode_responses=False) + heartbeat_loop 태스크 spawn,
  종료 시 cancel + aclose
- 각 tests/test_worker.py: test_poll_once_increments_jobs_done 추가
  (image:flux / video:sora / music:suno / insta:_process_one mock)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019LV86jBozkNhSFXJA412fq

services/video-render/main.py

@@ -3,11 +3,14 @@ from __future__ import annotations
 
 import asyncio
 import logging
+import os
 from contextlib import asynccontextmanager
 
+import redis.asyncio as aioredis
 from fastapi import FastAPI
 
 import worker
+from _shared.heartbeat import heartbeat_loop
 
 logging.basicConfig(level=logging.INFO, format="%(asctime)s %(name)s %(levelname)s %(message)s")
 logger = logging.getLogger(__name__)
@@ -16,15 +19,19 @@ logger = logging.getLogger(__name__)
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     worker_task = asyncio.create_task(worker.worker_loop())
+    hb_redis = aioredis.from_url(os.getenv("REDIS_URL", "redis://192.168.45.54:6379"), decode_responses=False)
+    hb_task = asyncio.create_task(heartbeat_loop(hb_redis, "video-render", "render", worker.stats))
     logger.info("video-render lifespan 시작")
     try:
         yield
     finally:
-        worker_task.cancel()
-        try:
-            await worker_task
-        except asyncio.CancelledError:
-            pass
+        for t in (worker_task, hb_task):
+            t.cancel()
+            try:
+                await t
+            except asyncio.CancelledError:
+                pass
+        await hb_redis.aclose()
         logger.info("video-render lifespan 종료")