chore: code-review fixes (menu churn, split-mark range, mutex recovery)

[sam-powers]

A code-quality sweep following the security hardening pass (#57–#62). Three substantive fixes plus cosmetic cleanups — no behavior change for users, only correctness and robustness under edge cases.

Substantive

• App.tsx — register menu listeners once. The Tauri menu-event handlers close over document state (filePath, comments, …) and re-create on most keystrokes, so the wiring effect tore down and re-listened all ten listeners every render. Now the handlers live in a ref refreshed per render and the listeners register once ([] deps), read live through the ref.
• TrackChanges.ts (getTrackedChanges) — guard range extension on contiguity. A tracked id is minted across a single contiguous run, so the merge now extends to only when the next node carrying that id actually abuts the accumulated range (pos === existing.to). The old unconditional Math.max would, on a malformed doc with a non-adjacent node sharing an id, widen to across unmarked text in between. New test covers the split-across-text-nodes case (bolding part of a tracked insertion splits the text node while both halves keep the id — it must still surface one contiguous change).
• lib.rs — recover poisoned mutexes instead of panicking. The six ChildRegistry / PendingDeepLink / child-handle .lock().unwrap() sites now route through a lock_recover helper that takes the inner guard on poisoning. These guard plain data (a process handle, a registry map, a pending path) that stays valid across a panic, so recovering is correct and avoids cascading a panic out of a spawn or deep-link path. Also logs (debug) skipped non-JSON lines in the claude stream rather than dropping them silently.

Cosmetic

• CommentLayer.tsx: deduplicate the two identical anchor-lookup helpers into one parameterized getAnchorTopBy.
• useSuggestions.ts: drop redundant as const on status literals (already narrowed by Suggestion.status).

Checks

typecheck, eslint, prettier, vitest (255 pass — +1 new), cargo fmt --check, clippy -D warnings, cargo test (35 pass) all green locally.

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