feat(ui): shortcut registry foundation (#652)

* feat(ui): shortcut registry foundation

Salvages the foundation of #380 by @gjermundgaraba — the original PR sat
6 weeks waiting for review and was closed by the author. This lands the
engine, scope data, and auto-generated marketing docs page, deferring
per-component handler migration to follow-up PRs.

Layout:
- packages/ui/shortcuts/{core,runtime,index}.ts — engine + barrel
- packages/ui/shortcuts/plan-review/* — scopes for plan editor surfaces
- packages/ui/shortcuts/code-review/* — scopes for review editor surfaces
- packages/{editor,review-editor}/shortcuts.ts — per-app surface composition
- apps/marketing/src/{components,lib} — auto-generated docs page

App behavior is unchanged: existing ad-hoc keydown handlers keep running.
The registry is plumbing waiting for migration PRs to wire to it.

Co-authored-by: Gjermund Garaba <gjermund@garaba.net>

* feat(ui): add missing shortcuts; warn on hold-binding gap

Addresses code review on #652.

Adds five live shortcuts that were missing from the registry, so the
auto-generated /docs/reference/keyboard-shortcuts page is no longer
incomplete:

- Mod+P (print plan)            — plan review + annotate
- Mod+B (toggle file tree)      — code review (new "Layout" section)
- Mod+. (toggle review sidebar) — code review
- Mod+Shift+T (toggle demo tour, dev-only) — code review
- Mod+Shift+F (focus PR comments search)   — new code-review/prComments scope

Also whitelists `.` as a valid normalized binding token in the registry
validator (keeps catching typos like Cmd/Ctrl while allowing legitimate
punctuation keys).

Hold-binding gap: the registry's `Alt hold` advertises a shortcut that
`useShortcutScope` cannot dispatch. Today this is harmless because the
existing `useInputMethodSwitch` hook handles it bespoke. Added warning
comments at the binding declaration and next to `useDoubleTapShortcuts`
so future migrators don't fall in. A `useHoldShortcuts` hook is the
proper fix and will land with the App.tsx migration that needs it.

* feat(ui): comprehensive shortcut registry coverage

Two-Sonnet inventory audit found 19 more user-facing shortcuts not in
the registry, on top of the 5 added in the previous commit. Adding all
of them so the auto-generated /docs/reference/keyboard-shortcuts page
ships honest and the in-app help modal (once migrated to read from the
registry) is comprehensive.

Plan / annotate surface (4 added):
- Escape closes image lightbox       (Viewer)
- Mod+Enter saves annotation edit    (AnnotationPanel)
- Escape cancels annotation edit     (AnnotationPanel)
- Enter confirms image name          (ImageAnnotator name field)

Code review surface (15 added):
- v / a in single-file diff mode     (toggle viewed / stage)
- v, a, x, z, c, [, ] in all-files   (new AllFilesDiff scope)
- Mod+Enter / Escape / Tab           (new SuggestionModal scope)
- Mod+Enter / Escape                 (new AI Assistant scope: AITab + AskAIInput)
- Escape closes tour dialog          (new TourDialog scope)

Engine: extended NAMED_TOKENS with `[` and `]` for the all-files
navigation bindings.

Tests updated for the new section ordering. App behavior unchanged —
this is pure declarative metadata. The existing ad-hoc keydown handlers
keep running; the registry is plumbing for the migration follow-up PRs.

* fix(ui): suggestion modal scope advertised non-existent submit shortcut

Self-review caught: SuggestionModal.tsx only has Escape (close) and Tab
(indent) handlers — no Mod+Enter. The Mod+Enter the inventory agent
referenced lives in AnnotationToolbar's suggested-code textarea, which
is already covered by reviewAnnotationToolbarShortcuts.submitComment.

Removed the bogus submit action from the scope. Renamed cancel→close
since the modal preserves suggestion state on Escape (it's not a
discard).

* fix(review): remove broken Cmd+Shift+C copy-diff shortcut

The handler at App.tsx:695 checked `e.key === 'c'` but Shift forces
`e.key` to uppercase `'C'`, so the shortcut never fired. The in-app
help modal also advertised it incorrectly as "Toggle comment mode".

Removing the broken shortcut entirely rather than fixing the case
mismatch — the toolbar's Copy button already does the same thing,
and there's no evidence anyone was relying on the keyboard shortcut.

Three deletions:
- packages/review-editor/App.tsx — handler block
- packages/review-editor/shortcuts.ts — copyDiff registry action
- packages/ui/components/KeyboardShortcuts.tsx — help modal entry

* chore(ui): address review nits

- F3: refresh AGENTS.md scope inventory (added scopes were missing)
- F5: getShortcutPlatform() now delegates to packages/ui/utils/platform
       isMac instead of duplicating the regex+SSR guard
- F7: drop the stand-alone imageAnnotator.confirmName entry; the
       behaviour is folded into the existing save action's hint so the
       marketing docs page no longer renders two Enter rows with
       different descriptions
- F8: remove the unused listenerOptions parameter from useShortcutScope
       (no callers; inline objects in the dep array would have caused
       re-render loops if anyone tried to use it)

TODOs left for the migration follow-up:
- F2: cross-scope arbitration — dispatchShortcutEvent should bail on
       event.defaultPrevented; needs preventDefault to be claimed
       consistently across scopes first
- F6: matchesKeyToken doesn't actually match the Space token; needs a
       special case before any scope binds Space

App behaviour unchanged.

---------

Co-authored-by: Gjermund Garaba <gjermund@garaba.net>

packages/review-editor/package.json

@@ -4,7 +4,8 @@
   "type": "module",
   "exports": {
     ".": "./App.tsx",
-    "./styles": "./index.css"
+    "./styles": "./index.css",
+    "./shortcuts": "./shortcuts.ts"
   },
   "dependencies": {
     "@pierre/diffs": "^1.1.12",