fix(core): route shared-sidecar callbacks by VM ownership

[DevEverything01]

• Shared sidecars retain one process-wide callback handler, so creating or disposing a VM can redirect or remove a sibling VM's host-function or filesystem-bridge handler.
• Dispatch host_callback and js_bridge_call by the frame's VM ownership. Reject unknown or removed VM routes, keep connection/session handlers, and remove VM handlers after teardown. Bound the TypeScript transport's dispatcher table and document its local configuration.
• Add both callback-type regressions, a real three-VM shared-sidecar regression, and a NativeKernel lifecycle regression.
• macOS arm64 validation: build, type checks, changed-file Biome, 19 protocol tests, Rust client contracts, and secure-exec tests pass. Full Core/Runtime Core lanes retain 8/1 failures also reproduced on clean main. Global Biome, publish-helper tests, and workspace Clippy have separately recorded main-baseline failures.

Related: shared sidecars #1531. #1926 addresses execution events; this change addresses sidecar requests. Execution-wait cancellation is prepared separately.

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