feat(ui): enhance panel resizing and state persistence

This update introduces functionality for resizing various panels in the UI, including the left sidebar, branch panel, stash panel, and file history. It also adds state persistence for panel sizes and collapsed states using local storage, improving user experience by maintaining preferences across sessions.

- Implemented resizing functionality for multiple UI panels
- Added local storage support for panel dimensions and collapsed states
- Enhanced accessibility features for panel controls

src/lib/components/BranchPanel.svelte

@@ -57,6 +57,8 @@
     onCreateTag: (name: string, message: string) => void | Promise<void>;
     onDeleteTag: (tag: GitTag) => void | Promise<void>;
     onPushTag: (tag: GitTag) => void | Promise<void>;
+    collapsed?: boolean;
+    onToggleCollapsed?: () => void;
   }
 
   let {
@@ -75,6 +77,8 @@
     onCreateTag = () => {},
     onDeleteTag = () => {},
     onPushTag = () => {},
+    collapsed = false,
+    onToggleCollapsed = () => {},
   }: Props = $props();
 
   let localOpen = $state(true);
@@ -355,7 +359,7 @@
 
 <svelte:window on:click={closeAllContextMenus} on:keydown={handleWindowKeydown} on:contextmenu|capture={closeAllContextMenus} />
 
-<section bind:this={panelElement} class="panel branch-panel grid grid-rows-[auto_1fr] overflow-hidden" aria-label="Branches">
+<section bind:this={panelElement} class="panel branch-panel grid grid-rows-[auto_1fr] overflow-hidden" class:collapsed aria-label="Branches">
   <div class="section-head">
     <div>
       <span class="eyebrow">Branches</span>
@@ -373,10 +377,26 @@
         <Plus size={14} aria-hidden="true" />
       </button>
       <span class="pill pill-count">{branches.length}</span>
+      <button
+        class="branch-create-toggle panel-collapse-toggle"
+        type="button"
+        onclick={onToggleCollapsed}
+        aria-expanded={!collapsed}
+        title={collapsed ? "Expand branches" : "Collapse branches"}
+        aria-label={collapsed ? "Expand branches panel" : "Collapse branches panel"}
+      >
+        {#if collapsed}
+          <ChevronRight size={14} aria-hidden="true" />
+        {:else}
+          <ChevronDown size={14} aria-hidden="true" />
+        {/if}
+      </button>
     </div>
   </div>
 
-  {#if !hasRepository}
+  {#if collapsed}
+    <!-- collapsed -->
+  {:else if !hasRepository}
     <p class="blank-state">Open a repository to list branches.</p>
   {:else if branches.length === 0 && tags.length === 0}
     <p class="blank-state">No branches returned.</p>