fix(steering): skip phantom zero-turn result on --resume; guard empty replies

On --resume, a background task stopped by the previous restart is replayed
as its own zero-turn turn with an empty result, before the real turn.
consume_stream took it as the answer -> empty Discord message (400) ->
"Sorry, something went wrong", while the real turn ran orphaned.

- stream_json: skip result with num_turns=0, empty, non-error
- router: empty Claude response becomes a visible notice, not an adapter crash

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014y1sJNe6mkWwFMwkWmCg8J

src/router.py

@@ -616,6 +616,11 @@ def route_message(
             # Same pattern as the existing __AUDIO__: sentinel — no
             # _set_last_response, the adapter reacts instead of replying.
             return response, False
+        if not (response or "").strip():
+            # Adapters can't send an empty message (Discord 400 → generic
+            # "something went wrong"); say so instead of failing opaquely.
+            log.warning("channel=%s: Claude returned an empty response", channel_id)
+            return "⚠️ Claude a terminat turul fără niciun răspuns text. Mai trimite o dată mesajul.", False
         _set_last_response(channel_id, response)
         return response, False
     except Exception as e: