feat(history): make branch filter groups collapsible

Add collapsible local and remote branch groups to the branch
visibility dialog, including toggle buttons and selection counts.
Introduce comprehensive dialog styling and responsive rules to match
the app UI. Opening the dialog now defaults to local open and remote
closed for faster access.

- Add CSS for branch-filter dialog layout, theming, and responsiveness
- Implement group toggles with chevrons and visible selected counts
- Default to local group open and remote group closed on dialog open

src/app.css

@@ -8523,3 +8523,152 @@ input:focus, textarea:focus, select:focus { box-shadow: 0 0 0 3px color-mix(in s
 :root[data-appearance="custom"] .graph-gutter {
   background: var(--color-surface-dim);
 }
+
+/* Branch visibility dialog ---------------------------------------------
+   Local and remote branches share one visual and interaction language. */
+.branch-filter-backdrop,
+:root[data-theme="light"] .branch-filter-backdrop {
+  padding: 24px;
+  background: var(--app-dialog-backdrop);
+  backdrop-filter: blur(5px);
+}
+
+.branch-filter-dialog,
+:root[data-theme="light"] .branch-filter-dialog {
+  width: min(560px, 100%);
+  max-height: min(680px, calc(100vh - 48px));
+  border-color: var(--color-border);
+  background: var(--app-dialog-bg);
+  box-shadow: var(--app-dialog-shadow);
+}
+
+.branch-filter-dialog-head {
+  min-height: 64px;
+  padding: 12px 14px;
+  border-bottom-color: var(--color-border);
+  background: var(--app-dialog-chrome);
+}
+
+.branch-filter-dialog-head h3 {
+  color: var(--color-ink);
+  font-size: 15px;
+}
+
+.branch-filter-summary {
+  min-height: 48px;
+  padding: 8px 14px;
+  border-bottom-color: var(--color-border);
+  color: var(--color-ink-muted);
+  background: var(--color-surface-dim);
+}
+
+.branch-filter-actions button {
+  min-height: 28px;
+  border-color: var(--color-border);
+  color: var(--color-ink-muted);
+  background: var(--color-surface-raised);
+}
+
+.branch-filter-actions button:hover:not(:disabled) {
+  border-color: var(--color-border-input);
+  color: var(--color-ink);
+  background: var(--color-surface-hover);
+}
+
+.branch-filter-dialog-list {
+  gap: 8px;
+  padding: 10px;
+  background: var(--color-surface-alt);
+}
+
+.branch-filter-group {
+  display: grid;
+  min-width: 0;
+  overflow: hidden;
+  border: 1px solid var(--color-border);
+  background: var(--color-surface);
+}
+
+.branch-filter-group-toggle {
+  display: grid;
+  grid-template-columns: 16px minmax(0, 1fr) auto;
+  align-items: center;
+  gap: 8px;
+  width: 100%;
+  min-height: 36px;
+  padding: 0 10px;
+  border: 0;
+  color: var(--color-ink-muted);
+  background: var(--color-surface-dim);
+  text-align: left;
+}
+
+.branch-filter-group-toggle:hover:not(:disabled) {
+  color: var(--color-ink);
+  background: var(--color-surface-hover);
+}
+
+.branch-filter-group-toggle > svg {
+  color: var(--color-accent);
+}
+
+.branch-filter-group-toggle > span {
+  font-size: 10px;
+  font-weight: 850;
+  letter-spacing: 0.09em;
+  text-transform: uppercase;
+}
+
+.branch-filter-group-toggle > em {
+  min-width: 34px;
+  padding: 2px 5px;
+  border: 1px solid var(--color-border-subtle);
+  color: var(--color-ink-faint);
+  background: var(--color-surface-raised);
+  font-size: 9px;
+  font-style: normal;
+  font-weight: 800;
+  text-align: center;
+}
+
+.branch-filter-group-list {
+  display: grid;
+  gap: 4px;
+  padding: 6px;
+  border-top: 1px solid var(--color-border-subtle);
+}
+
+.branch-filter-option,
+:root[data-theme="light"] .branch-filter-option,
+:root[data-theme="light"] .branch-filter-option.remote {
+  min-height: 34px;
+  border-color: color-mix(in srgb, var(--color-accent) 32%, var(--color-border));
+  color: var(--color-ink);
+  background: color-mix(in srgb, var(--color-accent) 8%, var(--color-surface-raised));
+  opacity: 1;
+}
+
+.branch-filter-option:hover,
+:root[data-theme="light"] .branch-filter-option:hover {
+  border-color: color-mix(in srgb, var(--color-accent) 52%, var(--color-border));
+  color: var(--color-ink);
+  background: color-mix(in srgb, var(--color-accent) 13%, var(--color-surface-hover));
+}
+
+.branch-filter-option.muted,
+:root[data-theme="light"] .branch-filter-option.muted {
+  border-color: var(--color-border-subtle);
+  color: var(--color-ink-faint);
+  background: var(--color-surface-raised);
+  opacity: 0.72;
+}
+
+.branch-filter-option input {
+  accent-color: var(--color-accent);
+}
+
+@media (max-width: 560px) {
+  .branch-filter-backdrop { padding: 8px; }
+  .branch-filter-summary { align-items: stretch; flex-direction: column; }
+  .branch-filter-actions { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); }
+}