fix: reinforce no-project-inference in system prompt; filter tool messages from title generation

src/fabledassistant/services/generation_task.py

@@ -122,10 +122,13 @@ async def _generate_title(messages: list[dict], user_id: int) -> str:
     # Build conversation text like summarize_conversation_as_note
     conv_lines = []
     for m in messages:
-        if m["role"] == "system":
+        if m["role"] in ("system", "tool"):
             continue
         label = "User" if m["role"] == "user" else "Assistant"
-        conv_lines.append(f"{label}: {m['content']}")
+        content = m.get("content", "")
+        if not content:
+            continue
+        conv_lines.append(f"{label}: {content}")
     # Keep only last 6 pairs worth of text
     conv_lines = conv_lines[-12:]