feat(05-03): add wireKeyboard() with all 7 keyboard shortcuts

- Space toggles play/pause, sends play/pause msg to server
- ArrowLeft/ArrowRight seek +/-5s, send seek msg, clear preview strips
- Ctrl+Z calls timeline.history.undo()
- Ctrl+Shift+Z and Ctrl+Y both call timeline.history.redo()
- Ctrl+S prevents browser dialog, fetches show and POSTs to save
- All shortcuts suppressed when focus is on input/select/textarea
- Space skips when active element is a button (prevents double-toggle)
- wireKeyboard() called at init after wireAudio()

lightsync/frontend/app.js

@@ -173,6 +173,77 @@ function wireAudio() {
     });
 }
 
+// ── Keyboard shortcuts ──────────────────────────────────────────────────────
+
+function wireKeyboard() {
+    const audio = document.getElementById('player');
+
+    document.addEventListener('keydown', (e) => {
+        // Skip shortcuts when typing in form elements
+        const tag = document.activeElement?.tagName?.toLowerCase();
+        if (['input', 'select', 'textarea'].includes(tag)) return;
+        // Also skip Space on focused buttons to prevent double-toggle (Pitfall 6)
+        if (e.code === 'Space' && tag === 'button') return;
+
+        if (e.code === 'Space') {
+            e.preventDefault();
+            if (!audio) return;
+            if (audio.paused) {
+                audio.play();
+                client.send({ type: 'play', position: audio.currentTime });
+            } else {
+                audio.pause();
+                client.send({ type: 'pause', position: audio.currentTime });
+            }
+        } else if (e.code === 'ArrowLeft') {
+            e.preventDefault();
+            if (!audio) return;
+            audio.currentTime = Math.max(0, audio.currentTime - 5);
+            client.send({ type: 'seek', position: audio.currentTime });
+            // Clear preview strips on seek
+            document.querySelectorAll('.device-strip').forEach(s => {
+                s.classList.remove('active');
+                const colorEl = s.querySelector('.strip-color');
+                if (colorEl) colorEl.style.backgroundColor = '';
+                const animEl = s.querySelector('.strip-anim');
+                if (animEl) animEl.textContent = '\u2014';
+            });
+        } else if (e.code === 'ArrowRight') {
+            e.preventDefault();
+            if (!audio) return;
+            audio.currentTime = Math.min(audio.duration || 0, audio.currentTime + 5);
+            client.send({ type: 'seek', position: audio.currentTime });
+            // Clear preview strips on seek
+            document.querySelectorAll('.device-strip').forEach(s => {
+                s.classList.remove('active');
+                const colorEl = s.querySelector('.strip-color');
+                if (colorEl) colorEl.style.backgroundColor = '';
+                const animEl = s.querySelector('.strip-anim');
+                if (animEl) animEl.textContent = '\u2014';
+            });
+        } else if (e.ctrlKey && !e.shiftKey && e.code === 'KeyZ') {
+            e.preventDefault();
+            timeline?.history.undo();
+        } else if ((e.ctrlKey && e.shiftKey && e.code === 'KeyZ') || (e.ctrlKey && e.code === 'KeyY')) {
+            e.preventDefault();
+            timeline?.history.redo();
+        } else if (e.ctrlKey && e.code === 'KeyS') {
+            e.preventDefault();  // Prevent browser Save dialog (Pitfall 7)
+            if (timeline?.showId) {
+                fetch(`/api/shows/${timeline.showId}`)
+                    .then(r => r.json())
+                    .then(show => fetch('/api/shows', {
+                        method: 'POST',
+                        headers: { 'Content-Type': 'application/json' },
+                        body: JSON.stringify(show),
+                    }))
+                    .then(() => console.log('[save] show saved via Ctrl+S'))
+                    .catch(e => console.warn('[save]', e));
+            }
+        }
+    });
+}
+
 // ── File list ────────────────────────────────────────────────────────────────
 
 async function refreshFiles(selectPath) {
@@ -277,6 +348,7 @@ document.getElementById('add-device-form')?.addEventListener('submit', async (e)
 // ── Init ─────────────────────────────────────────────────────────────────────
 
 wireAudio();
+wireKeyboard();  // keyboard shortcuts (Phase 5)
 
 // ── Preview strip builder ────────────────────────────────────────────────────