Completes H2:
- comprehensiveness coverage tests: every REGISTRY command form has a
hint_id resolving to a hint.cmd.* block, and every runtime error class
resolves to a hint.err.* block (enforces ADR-0053 D6)
- ADR-0051 keybinding strip advertises F1 in the editing (leads) and
default states; +shortcut.hint label; 12 full-panel snapshots
re-accepted (status-bar line only)
- flip ADR-0053 -> implemented, requirements H2 + A1 -> [x], README
2498 pass / 1 ignored, clippy clean.