feat(hub-ui): assign keyboard shortcuts to dock group members

[SaKaNa-Y]

Resolves the "dock group members can never be assigned keyboard shortcuts" problem discussed in vitejs/devtools#501, following the approach @antfu proposed there: when a shortcut hits a group entry with no preferred member, the command palette offers the sub-docks so the flow stays keyboard-driven.

Two independent halves, one commit each.

fix: nested commands were unbindable

Every consumer of the command tree walked a single level of children. Dock group members sit two levels below the Docks command, so they had no row in Settings → Shortcuts to bind, no entry in the keybinding collector to fire, and no id the dispatcher could resolve. That depth-1 ceiling is the literal cause of "can never be assigned".

Traversal now lives in one place: walkCommands visits the tree depth-first with a 'skip'/'stop' visitor signal, shared by findCommandDeep, collectAllKeybindings, the shortcut-settings rows, and the palette's root flatten. filterCommandsByWhen keeps its own recursion, since it rebuilds a cloned tree per level.

The ceiling was also stated in the public type: children on both DevframeServerCommandInput and DevframeClientCommand documented "Two levels max (parent → children)". Both now read "nested arbitrarily deep", so the JSDoc a consumer hovers matches what the tree actually accepts.

The palette's flatten and drill-down stack move to state/palette.ts. showInPalette: 'without-children' now prunes a whole subtree rather than one level, and a row carries its full path for search while displaying only its immediate parent.

feat: activating a group no longer guesses a member

A group has no view of its own, so activating one by id used to fall back to whichever member came first. A group whose members are peers has no member worth picking.

Activating a group command now opens an unambiguous target directly: the member last opened in that group, the author's defaultChildId, or a lone visible member. With several visible peers and no preferred member, it opens the palette drilled into that group. Pressing the same shortcut again closes the palette; stepping back to the root list unscopes it, so the shortcut drills back in rather than toggling.

CommandsContext gains openPalette(atCommandId?) and paletteScopeId. Members hang directly off their group in the command tree — the dock rail's sub-category dividers have no counterpart there, since a category is not something you can run. A group with no visible member and no reachable preferred member registers no command at all.

switchEntry remains on the programmatic path used by boot restore and hub:docks:activate: last-opened member, then defaultChildId, then the first registered member. The dock rail opens the last-opened or default member and reveals the member popover when neither resolves.

Picking a member through the scoped palette also raises it into the recent-dock slot from #305, with no extra wiring: that feature watches the selection rather than the dock rail's click handlers, so a keyboard-driven pick lands in the same slot a popover pick does.

Verification

Rebased onto main at a55f3d5. Full-repo ESLint and Knip are clean; typechecks for @devframes/hub and @devframes/hub-ui pass; direct builds for devframe, @devframes/hub, and every @devframes/hub-ui output pass.

Focused state tests: 4 files, 50 passing. Package suites: @devframes/hub has 164 passing / 1 skipped; @devframes/hub-ui has 59 passing. Full Vitest run: 122 files passing, 1 failing; 1348 tests passing, 14 skipped.

The remaining failure is the existing Windows-only @devframes/plugin-code-server fixture handoff (ENOENT … Temp\dcs-dump-*\hashed). It reproduces outside this PR and is unrelated to the hub command changes.

New specs: state/keybindings.test.ts (traversal, skip/stop, deep lookup), state/palette.test.ts (showInPalette pruning, path/parent titles, scope-trail degradation), and group-activation cases in state/context.test.ts. New stories: Commands/Palette → ScopedToGroup, Views/Builtin/Settings → DeeplyNestedShortcuts.

Docs: an "Activating a group" section and a "Nested commands" section in the hub guide, plus the openPalette / paletteScopeId API in the Hub API reference. New prose and comments follow the Terms vocabulary from #298 (dock rail, a devframe rather than a bare "host").

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[SaKaNa-Y]

Implemented the review follow-ups in e22596d. The command palette now executes actionable dock-group commands while preserving drill-down for ordinary command parents, keeps scope and breadcrumbs synchronized with the live command tree, and avoids stale registered actions. The headless client runtime now resolves nested client actions and default keybindings at arbitrary depth. Added regression coverage for group scope transitions, live command replacement, and grandchild commands. Validation: 50 focused tests passed; hub and hub-ui typechecks passed; ESLint and git diff checks passed.