docs(quick-16): complete Ctrl+A select-all hotkey implementation

.planning/quick/16-add-ctrl-a-hotkey-to-multi-select-views-/16-SUMMARY.md

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+---
+phase: quick-16
+plan: 01
+subsystem: frontend/keyboard-shortcuts
+tags: [shortcuts, selection, ctrl-a, multi-select]
+dependency_graph:
+  requires: [selection-controller, keyboard-shortcut-service]
+  provides: [select-all-shortcut]
+  affects: [track-list, queue-panel, playlist-view]
+tech_stack:
+  added: []
+  patterns: [CustomEvent broadcast for panel-agnostic shortcuts]
+key_files:
+  created: []
+  modified:
+    - frontend/src/utils/selection-controller.ts
+    - frontend/src/services/keyboard-shortcut-service.ts
+    - frontend/src/components/track-list/track-list.ts
+    - frontend/src/components/queue-panel/queue-panel.ts
+    - frontend/src/components/playlist-view/playlist-view.ts
+decisions:
+  - Broadcast shortcut:select-all to all connected components rather than routing to focused panel — harmless no-op on empty/inactive panels, consistent with existing tracklist.play pattern
+metrics:
+  duration: 2 min
+  completed: "2026-03-07"
+---
+
+# Quick Task 16: Add Ctrl+A Hotkey to Multi-Select Views
+
+SelectionController.selectAll() method with shortcut:select-all CustomEvent broadcast to track-list, queue-panel, and playlist-view
+
+## What Changed
+
+### Task 1: Add selectAll() to SelectionController and change app.selectAll dispatch
+**Commit:** `f567762`
+
+- Added `selectAll()` method to `SelectionController` that iterates all host items via `getItemCount()`/`getItemKey()` and builds a complete selection set
+- Includes early-return guard when all items are already selected (prevents redundant updates)
+- Sets `lastSelectedIndex` to the last item for consistent shift-click behavior after select-all
+- Changed `app.selectAll` dispatch from `document.execCommand('selectAll')` (browser text selection) to `document.dispatchEvent(new CustomEvent('shortcut:select-all'))` following the existing shortcut event pattern
+
+### Task 2: Wire select-all event listener in track-list, queue-panel, and playlist-view
+**Commit:** `906ea28`
+
+- Added `handleSelectAll` arrow method to all three components calling `this.selection.selectAll()`
+- Registered `shortcut:select-all` event listener in `connectedCallback()` and cleaned up in `disconnectedCallback()` for all three components
+- All three components may respond simultaneously but this is harmless — empty/inactive panels have 0 items and the selectAll early-return guard triggers immediately
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Verification Results
+
+| Check | Result |
+|-------|--------|
+| TypeScript compilation (`tsc --noEmit`) | Pass |
+| Lint (`make lint`) | Pass (0 issues) |
+| Pre-commit hooks | Pass (frontend-typecheck) |
+
+## Commits
+
+| Task | Commit | Description |
+|------|--------|-------------|
+| 1 | `f567762` | Add selectAll() to SelectionController and dispatch shortcut:select-all event |
+| 2 | `906ea28` | Wire shortcut:select-all listener in track-list, queue-panel, and playlist-view |
+
+## Self-Check: PASSED
+
+- All 5 modified files exist on disk
+- Both commits (f567762, 906ea28) verified in git log
+- SUMMARY.md created at expected path