feat(review-center): add repository filter and SelectMenu option meta/icon

Add a repository picker to the Review Center and wire it into the request
filtering logic. Introduces repositoryFilter state and a derived
repositoryOptions list (grouped by owner and carrying counts). If the
chosen repository disappears from the options, the filter is cleared
automatically.

Enhance SelectMenu to support per-option meta text and an optional
optionIcon snippet. Render options as [icon] label [meta] with updated
markup and CSS to align and style icon/label/meta. Adjust toolbar grid
and responsive CSS to make room for the new repository picker and to
tweak select popup/option styles.

src/app.css

@@ -298,9 +298,9 @@
     text-align: center;
   }
   .select-menu-option {
-    display: grid;
-    grid-template-columns: minmax(0, 1fr) 14px;
+    display: flex;
     align-items: center;
+    gap: 8px;
     justify-content: initial;
     width: 100%;
     min-height: 30px;
@@ -314,6 +314,25 @@
     text-align: left;
   }
   .select-menu-option > span { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+  .select-menu-option-label { flex: 1 1 auto; min-width: 0; }
+  .select-menu-option-icon {
+    display: grid;
+    flex: 0 0 auto;
+    place-items: center;
+    width: 18px;
+    overflow: visible;
+    color: var(--color-ink-faint);
+  }
+  .select-menu-option.selected .select-menu-option-icon,
+  .select-menu-option:hover .select-menu-option-icon { color: var(--color-accent); }
+  .select-menu-option-icon svg { color: inherit; }
+  .select-menu-option-meta {
+    flex: 0 0 auto;
+    color: var(--color-ink-faint);
+    font-size: 9.5px;
+    font-weight: 650;
+    letter-spacing: 0;
+  }
   .select-menu-option svg { color: var(--color-primary); }
   .select-menu-option:hover:not(:disabled), .select-menu-option.active:not(:disabled) {
     border-color: var(--color-border-subtle);