keyboard-operable ClideTappable + palette nav (T-100)

Plug widgets into the keymap layer landed in T-117.

ClideTappable:
  - Wrap in `Actions(ActivateIntent → onTap)` outside a `Focus` so
    dispatch from the focused context walks up and hits the action.
  - Add a focus ring via `tokens.globalFocus` (DecoratedBox foreground
    overlay, transparent border when unfocused, no layout shift).
  - Disabled (`onTap == null`) skips focus traversal and shows the
    forbidden cursor.

ClidePalette:
  - Register Actions for the four palette intents
    (selectNext / selectPrev / accept / dismiss).
  - Publish `palette.open` scope flag via `KeymapService.setScopeFlag`
    so when-clauses can scope future bindings to "palette only".
  - Highlight the selected row with `listItemSelectedBackground`;
    scroll it into view on nav.
  - `PaletteController` grows `selectedIndex` + `selectNext` /
    `selectPrevious` / `acceptSelected`; index resets on open /
    filter change.

Intents.dart drops the `ClideIntent` base — `ActivateIntent` and
`DismissIntent` come from Flutter; clide owns the palette and text-
scale and command-bridge subclasses. `parseIntentId('activate')` →
Flutter's class; same for dismiss. Widget code uses the canonical
Flutter Intent types where they fit.

App root grows a PaletteOpenIntent action that calls
`services.palette.open()`, completing the ctrl/cmd+shift+p path
end-to-end.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -48,6 +48,9 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
   VS-Code-style when-clauses, layered preset → user file → settings
   overlay. Default preset ships; vim/vscode/jetbrains unblocked
   (T-117, supersedes T-110).
+- Keyboard operability — `ClideTappable` is now Tab-focusable with a
+  focus ring and Enter/Space activation; `ClidePalette` adds arrow
+  nav, Escape dismiss, and selection highlight (T-100).
 - Test sweep — `keybindings`, `toolchain_paths`, and several
   `widgets/src/` primitives (tooltip, palette, multitab, markdown).
 - `tree_sitter_service` sweep — fake-FFI + real-library smoke,