fix: force JSON output from Groq to prevent JSONDecodeError

Add response_format={"type":"json_object"} to Groq API call so the
model always returns structurally valid JSON. Add a regex fallback
extractor as a second safety net for any edge cases.

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

services/story_service.py

@@ -97,16 +97,26 @@ async def generate_episode(
             {"role": "user",   "content": prompt},
         ],
         temperature=0.92,
-        max_tokens=4000,  # 20 scenes need more tokens
+        max_tokens=4000,
+        response_format={"type": "json_object"},
     )
 
     raw = resp.choices[0].message.content.strip()
 
-    # Strip markdown fences if model added them
+    # Strip markdown fences if model added them anyway
     raw = re.sub(r"^```(?:json)?\s*", "", raw, flags=re.MULTILINE)
     raw = re.sub(r"\s*```$",          "", raw, flags=re.MULTILINE)
 
-    data = json.loads(raw)
+    # Try parsing; if it fails extract the outermost JSON object as a fallback
+    try:
+        data = json.loads(raw)
+    except json.JSONDecodeError:
+        # Find the first { ... } blob and try again
+        m = re.search(r"\{.*\}", raw, re.DOTALL)
+        if m:
+            data = json.loads(m.group(0))
+        else:
+            raise
 
     # Sanitize text — strip markdown bold/italic/etc
     def clean(s: str) -> str: