feat(command-palette): add recently used section and switch-player commands

Adds a "Recently used" section at the top of the command palette (capped at 5,
persisted via StorageMap) and five "Switch player to ..." commands for one-step
player switching from anywhere. MPV/VLC are gated to Electron; the active player
entry is shown disabled. Switching applies to the next playback session.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Entire-Checkpoint: c2cea9c530e6

docs/architecture/workspace-shell.md

@@ -131,6 +131,18 @@ Command palette behavior is shell-owned but view-extensible:
    metadata through `WorkspaceHeaderContextService`.
 5. Filtering matches command labels, descriptions, and keywords, and keyboard
    selection always lands on the first enabled command.
+6. A "Recently used" section is rendered above the standard groups when the
+   query is empty and at least one stored id resolves to a visible+enabled
+   command; ids are persisted via `RecentCommandsService` (capped at 5,
+   stored at `STORE_KEY.RecentCommands`). Storage is **not** pruned by route
+   visibility — a navigation command like `Open sources` is invisible while
+   the user is on `/workspace/sources` but the id stays in storage so it
+   reappears in the recent section after navigating away.
+7. Five "Switch player to X" commands are registered globally by
+   `WorkspacePlayerCommandsContributor`. The MPV/VLC entries are visible only
+   in Electron, and the entry matching the current `SettingsStore.player()`
+   value is disabled. The new player setting applies to the next playback
+   session; an existing stream is not re-mounted.
 
 ## Maintenance Guidance