fix(ipc): auto-claim shm client slots

[charlielye]

Summary

• make MPSC SHM clients self-allocate a free producer slot when no explicit client id is provided
• pass omitted TS/NAPI client ids through to the native auto-claim path instead of defaulting to slot 0
• add C++ and world-state regression tests for multi-client SHM response correlation and clean slot reuse

Why

Multiple SHM clients were defaulting to producer slot 0. In the wsdb/AVM topology that means separate clients can share one request/response ring pair and steal or mis-correlate responses. The fix adds a small owner table to the existing MPSC doorbell mapping so clients can atomically claim distinct slots.

This intentionally does not try to recover stale in-flight requests left by a crashed client. Clean disconnect releases the claimed slot for reuse.

Validation

• cmake --build build --target ipc_runtime_tests -j
• ./build/ipc_runtime_tests --gtest_filter='ShmTest.MpscReactorMultiClientResponseRouting:ShmTest.MpscReactorAutoClaimMultiClient:ShmTest.MpscSlotFreedOnDisconnectAndReclaimed'

Note: the fresh next-based worktree had no yarn install state, so the TS world-state test is left for CI here. It passed earlier in the existing built ipc-5 worktree before this was split into a standalone PR.