Add convey.emit() for non-blocking Callosum events from routes
Adds emit() function to convey/bridge.py that reuses the shared
CallosumConnection for sending events. Non-blocking with drop-on-disconnect
semantics - messages queue for background thread, dropped if disconnected.
- Export emit() from convey package
- Migrate apps/import and apps/remote from callosum_send() to emit()
- Document server-side events in APPS.md and CALLOSUM.md
- Update bridge.py docstring for bidirectional capability
- Remove unused timeout parameter from stop_bridge()
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>