refactor: harden repository views and runtime performance

[whackur]

Summary

• split repository/session state into explicit catalog, log, repository-view, and git-load controllers
• move expensive git views off the UI thread with bounded, fair, recoverable worker lifecycle
• add dirty-frame rendering, diff render caches, terminal inbox backpressure, and large viewer virtualization
• preserve viewer identity, session restore state, hot-file fade deadlines, and stale-generation guards
• include the fork's existing terminal resize convergence and comment cleanup commits

Verification

• cargo fmt --all --check
• cargo build
• cargo test (1,690 passed; 4 ignored on Windows)
• cargo clippy --all-targets --all-features -- -D warnings
• npm --prefix viewer-ui test (397 passed)
• npm --prefix viewer-ui run build (embedded dist clean)
• docker compose run --rm unix-gate (ALL GATES PASSED)
• independent semantic and security reviews, with all actionable findings resolved
• Hermes nightcrow Kanban: 10 done, 0 active