feat: improve generation analytics and maintenance

backend/app/core/config.py

@@ -62,12 +62,20 @@ class Settings(BaseSettings):
         False,
         description="Enable local deterministic demo providers for portfolio demos",
     )
-    story_audio_cache_dir: str = Field(
-        "storage/audio",
-        description="Directory for cached story audio files",
-    )
-
-    # Celery (Redis)
+    story_audio_cache_dir: str = Field(
+        "storage/audio",
+        description="Directory for cached story audio files",
+    )
+    story_audio_cache_ttl_days: int = Field(
+        30,
+        description="TTL in days before cached story audio is pruned",
+    )
+    generation_job_stale_minutes: int = Field(
+        60,
+        description="Minutes before a running generation job is considered stale",
+    )
+
+    # Celery (Redis)
     celery_broker_url: str = Field("redis://localhost:6379/0")
     celery_result_backend: str = Field("redis://localhost:6379/0")