feat(hint): H2 Phase D — coverage gate, F1 strip, status flips (ADR-0053)

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.

docs/adr/0053-contextual-hint-command-and-keybinding.md

@@ -2,7 +2,15 @@
 
 ## Status
 
-Accepted — implementation in progress. Revised after a `/runda` review
+Accepted — **implemented 2026-06-15** (plan:
+`docs/plans/20260614-adr-0053-contextual-hint-H2.md`; the F1 keybinding +
+`hint` command, the `hint_ids` per-form keying + `hint_key_for_input_in_mode`,
+`last_error_hint_key` + `friendly::error_hint_class`, the `note_hint*`
+renderers, and the `hint.cmd.*`/`hint.err.*` corpus for every command form
++ the 9 runtime error classes, with the comprehensiveness coverage test
+and the ADR-0051 strip advertising F1). Closes **A1** + requirements
+**H2**. Deferred: the pre-submit-diagnostic route + `diagnostic.*` blocks
+(#38), clause-concept hints (#37). Revised after a `/runda` review
 (2026-06-14): corrected the verbosity-default fact; re-keyed tier-3
 content off `help_id`; split the pre-submit-diagnostic and runtime-error
 paths; added a comprehensiveness coverage test. Revised again during