fix: tool registry emits Anthropic schema, question lifecycle cleanup

- Tool.to_schema() emits input_schema (Anthropic Messages API) instead
  of OpenAI-style parameters
- QuestionManager: remove questions from _pending on answer and timeout,
  reject double answers, add list_pending()
- core/skills/__init__.py so skills are importable as a package
- revert optional-import fallbacks in logger/message_bus: nats-py and
  loguru are hard requirements, a broken install should fail loudly
- tests for wait_for_answer happy path and timeout cleanup

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012AJLYcbTHCe45fyFnMfEin

core/interactive_question.py

@@ -110,24 +110,33 @@ class QuestionManager:
             raise TimeoutError(f"Question {question.question_id} timed out waiting for human input")
         finally:
             self._futures.pop(question.question_id, None)
+            self._pending.pop(question.question_id, None)
 
     def answer_question(self, question_id: str, answer: Any) -> bool:
-        """Called when human operator submits an answer from the UI."""
+        """Called when human operator submits an answer from the UI.
+
+        Returns False if the question is unknown or was already answered."""
         question = self._pending.get(question_id)
         if not question:
             logger.warning(f"No pending question found for id {question_id}")
             return False
+        if question.answered:
+            logger.warning(f"Question {question_id} already answered; ignoring")
+            return False
 
         question.answered = True
         question.answer = answer
 
         fut = self._futures.get(question_id)
         if fut and not fut.done():
-            fut.set_result(answer)
-            return True
-
+            fut.set_result(answer)  # wait_for_answer() removes it from _pending
+        else:
+            self._pending.pop(question_id, None)  # nobody waiting; don't leak
         return True
 
+    def list_pending(self) -> List[Question]:
+        return [q for q in self._pending.values() if not q.answered]
+
     def get_pending(self, question_id: str) -> Optional[Question]:
         return self._pending.get(question_id)