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/lib/components/SelectMenu.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import type { Snippet } from "svelte";
   import { tick } from "svelte";
   import { Check, ChevronDown, Search } from "@lucide/svelte";
 
@@ -7,6 +8,8 @@
     label: string;
     group?: string;
     disabled?: boolean;
+    /** Small right-aligned text, e.g. a count. */
+    meta?: string;
   }
 
   interface Props {
@@ -20,6 +23,8 @@
     searchable?: boolean;
     searchPlaceholder?: string;
     emptyText?: string;
+    /** Optional icon in front of every option, e.g. a branch or repository mark. */
+    optionIcon?: Snippet<[SelectMenuOption]>;
     onChange: (value: string) => void;
   }
 
@@ -34,6 +39,7 @@
     searchable = false,
     searchPlaceholder = "Search…",
     emptyText = "No results",
+    optionIcon = undefined,
     onChange,
   }: Props = $props();
 
@@ -187,7 +193,9 @@
           onmouseenter={() => { if (!option.disabled) activeIndex = index; }}
           onclick={() => choose(index)}
         >
-          <span>{option.label}</span>
+          {#if optionIcon}<span class="select-menu-option-icon">{@render optionIcon(option)}</span>{/if}
+          <span class="select-menu-option-label">{option.label}</span>
+          {#if option.meta}<small class="select-menu-option-meta">{option.meta}</small>{/if}
           {#if option.value === value}<Check size={14} aria-hidden="true" />{/if}
         </button>
       {/each}