feat: add Prometheus metrics + fix CI/CD health check port

- Add prometheus-client dependency
- Create middleware/metrics.py with PrometheusMiddleware
- Expose /metrics endpoint in Prometheus text format
- Track http_requests_total, translation_total, translation_duration_seconds,
  file_size_bytes
- Instrument translate routes with record_translation() and record_file_size()
- Fix deploy.yml health check: localhost:8000 -> localhost:8001 (Portainer conflict)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

routes/translate_routes.py

@@ -60,6 +60,7 @@ from schemas.translation import (
 )
 from schemas.errors import ErrorResponse
 from utils.file_handler import FileHandler
+from middleware.metrics import record_translation, record_file_size
 from services.progress_tracker import ProgressTracker
 from services.storage_tracker import storage_tracker
 from core.redis import set_job_status_async, get_job_status_async
@@ -696,6 +697,10 @@ async def translate_document_v1(
 
         _cleanup_old_jobs()
 
+        # Record file size metric
+        if file_extension and file_size:
+            record_file_size(file_extension, file_size)
+
         _translation_jobs[job_id] = {
             "id": job_id,
             "status": "queued",
@@ -1124,10 +1129,15 @@ async def _run_translation_job(
                     logger.warning(f"Job {job_id}: watermark failed: {wm_err}")
 
         tracker.set_completed(str(output_path))
+        # Record translation metric
+        duration = time.time() - time.mktime(datetime.fromisoformat(job["created_at"].replace("Z", "+00:00")).timetuple())
+        record_translation(provider=provider, file_type=file_extension or "unknown", duration=duration, status="success")
         logger.info(f"Job {job_id}: Completed successfully")
 
     except Exception as e:
         tracker.set_error(str(e))
+        # Record translation failure metric
+        record_translation(provider=provider, file_type=file_extension or "unknown", duration=0, status="error")
         logger.error(f"Job {job_id}: Failed - {e}")
 
     finally: