Gateway archive embedder now parses metadata.channel.{channelName,threadName}
from each message and stores channel_name/thread_name in the Qdrant payload.
Backend exposes them; the semantic results card renders the thread name (or
channel name) instead of a raw #snowflake, with the ID as a last-resort
fallback for legacy points. Matches the message feed's channel-label logic
(getMessageChannelLabel).