fix: Make debug parameter work as Query parameter in /api/prompts/execute

Bug: debug=true in URL was ignored because FastAPI expected it in
request body (POST without Query() expects body params by default).

Result: node_states were never returned, even with ?debug=true

Fix: Changed debug and save to Query parameters:
- debug: bool = Query(False, ...)
- save: bool = Query(False, ...)

Now ?debug=true in URL correctly enables debug output with node_states.

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

backend/routers/prompts.py

@@ -1447,11 +1447,11 @@ from models import UnifiedPromptCreate, UnifiedPromptUpdate
 
 @router.post("/execute")
 async def execute_unified_prompt(
-    prompt_slug: str,
+    prompt_slug: str = Query(..., description="Slug of prompt to execute"),
     modules: Optional[dict] = None,
     timeframes: Optional[dict] = None,
-    debug: bool = False,
-    save: bool = False,
+    debug: bool = Query(False, description="Include debug information (node_states, etc.)"),
+    save: bool = Query(False, description="Save result to ai_insights"),
     session: dict = Depends(require_auth)
 ):
     """