feat(debug): add MQTT_RAW_LOG env switch for unfiltered RX logging

Logs every incoming MQTT message on INFO regardless of topic, including
dedup'd duplicates and topics with no registered callback - useful for
capturing printer behavior the bridge doesn't normally surface without
needing to know the topic name in advance (the existing wildcard
subscribe already receives everything, this just makes it visible).

kobrax_client.py

@@ -144,6 +144,11 @@ class KobraXClient:
 
         # Dedup: last hash per topic suffix to suppress repeated identical messages
         self._last_rx_hash: dict[str, str] = {}
+        # Debug switch (MQTT_RAW_LOG=1): logs every RX message unfiltered on
+        # INFO, including dedup'd duplicates and topics with no registered
+        # callback - for capturing printer behavior the bridge doesn't
+        # normally surface (e.g. reverse-engineering a rejected command).
+        self._raw_log = os.environ.get("MQTT_RAW_LOG", "").strip().lower() in ("1", "true", "yes")
         # Fields that change every tick and should be stripped before dedup-hashing
         _VOLATILE = {"timestamp", "msgid", "progress", "curr_layer",
                      "curr_nozzle_temp", "curr_hotbed_temp",
@@ -422,6 +427,9 @@ class KobraXClient:
     def _dispatch(self, topic: str, payload: dict):
         suffix = "/".join(topic.split("/")[-2:])
 
+        if self._raw_log:
+            log.info("RX [raw] %s  %s", topic, json.dumps(payload, ensure_ascii=False))
+
         # Structured RX log with dedup suppression
         h = self._dedup_hash(suffix, payload)
         is_dup = self._last_rx_hash.get(suffix) == h