feat(electrobun): settings overhaul — fonts, shells, providers, retention, chords

- Settings drawer: responsive width clamp(24rem, 45vw, 50rem)
- System font detection: fc-list for UI fonts (preferred sans-serif starred)
  and mono fonts (Nerd Fonts starred), fallback to hardcoded lists
- Scrollback: default 5000, min 1000, step 500
- Shell detection: system.shells RPC, pre-selects $SHELL login shell
- Provider enablement: provider.scan gates toggle, unavailable shown as N/A
- Session retention: count 0-100 (0=Keep all), age 0-365 (0=Forever)
- Chord keybindings: Ctrl+K → Ctrl+S style multi-key sequences,
  1s prefix wait, arrow separator display, 26 tests passing

ui-electrobun/tests/unit/keybinding-store.test.ts

@@ -202,10 +202,53 @@ describe('conflict detection', () => {
 
 describe('capture mode', () => {
   it('chordFromEvent records full chord for capture', () => {
-    // Simulate user pressing Ctrl+Shift+X in capture mode
     const chord = chordFromEvent({
       ctrlKey: true, metaKey: false, shiftKey: true, altKey: false, key: 'x',
     });
     expect(chord).toBe('Ctrl+Shift+X');
   });
 });
+
+// ── Chord sequence helpers ──────────────────────────────────────────────────
+
+function chordParts(chord: string): string[] {
+  return chord.split(' ').filter(Boolean);
+}
+
+function formatChord(chord: string): string {
+  return chordParts(chord).join(' \u2192 ');
+}
+
+describe('chord sequences', () => {
+  it('chordParts splits single chord', () => {
+    expect(chordParts('Ctrl+K')).toEqual(['Ctrl+K']);
+  });
+
+  it('chordParts splits multi-key chord', () => {
+    expect(chordParts('Ctrl+K Ctrl+S')).toEqual(['Ctrl+K', 'Ctrl+S']);
+  });
+
+  it('formatChord adds arrow separator', () => {
+    expect(formatChord('Ctrl+K Ctrl+S')).toBe('Ctrl+K \u2192 Ctrl+S');
+  });
+
+  it('formatChord passes through single chord', () => {
+    expect(formatChord('Ctrl+Shift+F')).toBe('Ctrl+Shift+F');
+  });
+
+  it('setChord stores chord sequence', () => {
+    const state = createKeybindingState();
+    state.setChord('palette', 'Ctrl+K Ctrl+P');
+    const b = state.getBindings().find(b => b.id === 'palette');
+    expect(b?.chord).toBe('Ctrl+K Ctrl+P');
+  });
+
+  it('conflict detection works with chord sequences', () => {
+    const state = createKeybindingState();
+    state.setChord('palette', 'Ctrl+K Ctrl+P');
+    state.setChord('settings', 'Ctrl+K Ctrl+P');
+    const conflicts = state.findConflicts('Ctrl+K Ctrl+P', 'palette');
+    expect(conflicts).toHaveLength(1);
+    expect(conflicts[0].id).toBe('settings');
+  });
+});