Cancel stale TUI speech synthesis

[hrhrng]

Summary

• interrupt obsolete command synthesis when sentence navigation replaces the speech route
• cooperatively cancel resident Qwen/MOSS/Kokoro requests without unloading their models
• suppress failures from stale speech eras so read-aloud remains active
• strengthen Manual isolation and repeated-left integration coverage under slow synthesis

Verification

• cargo test --locked
• cargo clippy --all-targets -- -D warnings
• cargo fmt --check
• Python compile check for all three shipped resident workers