fix: move /execute-stream route BEFORE /{prompt_id} catch-all (FastAPI route ordering)

Root cause: FastAPI matches routes in definition order. The /{prompt_id}
catch-all at line 257 was intercepting /execute-stream requests before
the specific route handler could match.

Fix: Moved execute-stream definition (with section header + imports)
to line 257, before the catch-all route (now at line 414).

This resolves the 'Connection to server lost' error in SSE streaming.

backend/routers/prompts.py

@@ -254,6 +254,11 @@ def import_prompts(
     }
 
 
+# ══════════════════════════════════════════════════════════════════════════════
+# UNIFIED PROMPT SYSTEM (Issue #28 Phase 2)
+# ══════════════════════════════════════════════════════════════════════════════
+
+from prompt_executor import execute_prompt_with_data
 from models import UnifiedPromptCreate, UnifiedPromptUpdate
 
 
@@ -403,9 +408,8 @@ async def execute_unified_prompt_stream(
             "Connection": "keep-alive",
             "X-Accel-Buffering": "no"  # Disable nginx buffering
         }
+    )
 
-# NOTE: /execute-stream MUST be defined BEFORE /{prompt_id} to avoid route conflicts
-# FastAPI matches routes in order, so specific routes must come before catch-all patterns
 
 @router.get("/{prompt_id}")
 def get_prompt(prompt_id: str, session: dict=Depends(require_auth)):
@@ -1590,15 +1594,7 @@ def reset_prompt_to_default(prompt_id: str, session: dict=Depends(require_admin)
     return {"ok": True}
 
 
-# ══════════════════════════════════════════════════════════════════════════════
-# UNIFIED PROMPT SYSTEM (Issue #28 Phase 2)
-# ══════════════════════════════════════════════════════════════════════════════
-
-from prompt_executor import execute_prompt_with_data
-    )
-
-
-
+@router.post("/execute")
 async def execute_unified_prompt(
     prompt_slug: str = Query(..., description="Slug of prompt to execute"),
     modules: Optional[dict] = None,