bridge: concurrent-session publisher missing — two Python bridges in the same workspace do not dedup

[ericleepi314]

File: src/bridge/repl_bridge_handle.py:52-56

# TODO(phase2): once src/utils/concurrent_sessions.py exists, call
#   update_session_bridge_id(get_self_bridge_compat_id())
# to publish the local bridge ID so other peers can dedup us out.

Background: The TS version calls utils/concurrentSessions.updateSessionBridgeId() on every set, publishing the local bridge ID so other peers can dedup. The Python port replaces this with a debug-logged no-op; src/utils/concurrent_sessions.py does not exist yet.

Impact: Two concurrent Python bridges in the same workspace will not dedup against each other — both appear in claude.ai/code session lists.

Fix sketch: Port utils/concurrentSessions (the bridge-ID publisher + reader), then replace the no-op in set_repl_bridge_handle with update_session_bridge_id(get_self_bridge_compat_id()). Related: src/transports/remote_io.py:142 has a TODO(parity) to wire session_id from bootstrap (currently always None), which the same module should resolve.