refactor(transport): isolate local byte-stream boundary

[jlongster]

Summary

• Extract a narrow local transport boundary for listener polling, connections, disconnect monitors, cancellation, and explicit response completion.
• Share daemon authentication, dispatch, subscriptions, ownership handling, and cleanup loop; keep Unix registration and endpoint filesystem wiring separate.
• Preserve protocol 7 and the current exclusive-owner/handoff state machine. Document the proposed opaque Windows named-pipe endpoint contract without claiming Windows transport support.
• Add Unix transport roundtrip/cancellation/final-frame regressions and daemon authentication/final-exit delivery coverage.

Verification

• cargo fmt --check passed.
• cargo clippy --locked --all-targets --all-features -- -D warnings passed.
• cargo test --locked passed locally: 26 library + 5 effects + 4 ownership + 3 playground + 1 rows + 10 service = 49 tests.
• printf "demo\nlist\nquit\n" | cargo run --locked -- play passed with QUERY_RESPONSE_OK and clean daemon exit.
• Native Windows x64/ARM64 and Linux/macOS CI will run on this PR. Windows support remains limited to the already-enabled tests in T1.

Stack

T1 of the Windows transport lane: master -> windows-transport -> windows-pipes -> windows-daemon. No merge requested; later tasks will be separate stacked PRs.

Native CI results (head 4bc952b)

• Windows x64 and ARM64: both passed; each 19 library + 5 effects tests, plus standalone library rerun. Unix-gated integration suites intentionally run zero tests here.
• Core: Linux 49 tests; macOS 45 tests; Miri 5 tests under each borrow model. Formatting and Clippy passed.