Code review 2026-09-24: terminal and app behaviour fixes #69

Part 2 of 3 (docs/superpowers/plans/2026-09-25-code-review-fixes.md): #2 warm-shell leak, #12 spawn/kill race, #4 dictation double paste, #6 layout-independent Ctrl+C/V, #9/#23 no remount on cd, #10 chords under dialogs, #20/#25 cell vs UTF-16 offsets, #21 Shift+Enter, #24 resume spinner on a failed spawn, #31 StrictMode double restore, #32 menu state across tabs, #33 drag leaving the window.