refactor: improve XMPP client/bridge architecture separation
- Move protocol normalization methods to XMPP client (ExtractChannelID, ExtractUserInfo, ExtractMessageBody)
- Replace message channel aggregation with direct handler delegation pattern
- XMPP client now focuses purely on protocol concerns (connection, deduplication, normalization)
- XMPP bridge handles business logic (BridgeMessage creation, routing)
- Add SourceRemoteID field to BridgeMessage for better message tracking
- Remove unused message channel infrastructure in favor of mux.MessageHandlerFunc pattern
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Co-Authored-By: Claude <noreply@anthropic.com>
Felipe Martin
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