feat: brain colored folders/tags — color + icon fields, mobile pills

Backend:
- Added color (hex) and icon (lucide name) columns to folders and tags
- Default folders seeded with colors: Home=green, Work=indigo, Travel=blue, etc.
- API returns color/icon in sidebar and CRUD responses
- Create/update endpoints accept color and icon

Frontend:
- Mobile: horizontal scrollable pill tabs with colored dots
- Desktop sidebar: colored dots next to folder names
- Active pill gets tinted border matching folder color

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend-v2/src/lib/pages/brain/AtelierBrainPage.svelte

@@ -23,8 +23,8 @@
     assets: { id: string; asset_type: string; filename: string; content_type: string | null }[];
   }
 
-  interface SidebarFolder { id: string; name: string; slug: string; is_active: boolean; item_count: number; }
-  interface SidebarTag { id: string; name: string; slug: string; is_active: boolean; item_count: number; }
+  interface SidebarFolder { id: string; name: string; slug: string; color?: string; icon?: string; is_active: boolean; item_count: number; }
+  interface SidebarTag { id: string; name: string; slug: string; color?: string; icon?: string; is_active: boolean; item_count: number; }
 
   let loading = $state(true);
   let items = $state<BrainItem[]>([]);
@@ -366,6 +366,7 @@
         <nav class="sidebar-nav">
           {#each sidebarFolders.filter(f => f.is_active) as folder}
             <button class="nav-item" class:active={activeFolder === folder.name} onclick={() => { activeFolder = folder.name; activeFolderId = folder.id; activeTag = null; activeTagId = null; mobileSidebarOpen = false; loadItems(); }}>
+              {#if folder.color}<span class="nav-dot" style="background: {folder.color}"></span>{/if}
               <span class="nav-label">{folder.name}</span>
               {#if showManage}
                 <!-- svelte-ignore a11y_no_static_element_interactions --><span class="nav-delete" onclick={(e) => { e.stopPropagation(); if (confirm(`Delete "${folder.name}"? Items will be moved.`)) deleteTaxonomy(folder.id); }}>×</span>
@@ -437,11 +438,20 @@
           {#if uploading}<div class="upload-status">Uploading...</div>{/if}
         </section>
 
-        <!-- Mobile sidebar toggle -->
-        <button class="mobile-filter-btn" onclick={() => mobileSidebarOpen = true}>
-          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round"><line x1="4" y1="21" x2="4" y2="14"/><line x1="4" y1="10" x2="4" y2="3"/><line x1="12" y1="21" x2="12" y2="12"/><line x1="12" y1="8" x2="12" y2="3"/><line x1="20" y1="21" x2="20" y2="16"/><line x1="20" y1="12" x2="20" y2="3"/></svg>
-          Folders & Tags
-        </button>
+        <!-- Mobile: horizontal pill filters -->
+        <div class="mobile-pills">
+          <button class="pill" class:active={!activeFolder && !activeTag} onclick={() => { activeFolder = null; activeTag = null; activeFolderId = null; activeTagId = null; mobileSidebarOpen = false; loadItems(); }}>
+            All
+          </button>
+          {#each sidebarFolders.filter(f => f.is_active) as folder}
+            <button class="pill" class:active={activeFolder === folder.name} onclick={() => { activeFolder = folder.name; activeFolderId = folder.id; activeTag = null; activeTagId = null; loadItems(); }}
+              style={folder.color ? `--pill-color: ${folder.color}` : ''}>
+              {#if folder.color}<span class="pill-dot" style="background: {folder.color}"></span>{/if}
+              {folder.name}
+              {#if folder.item_count > 0}<span class="pill-count">{folder.item_count}</span>{/if}
+            </button>
+          {/each}
+        </div>
 
         <!-- Active filter indicator -->
         {#if activeFolder || activeTag}
@@ -867,26 +877,56 @@
     overflow-x: hidden;
   }
 
-  /* ═══ Mobile filter button ═══ */
-  .mobile-filter-btn {
+  /* ═══ Mobile pills ═══ */
+  .mobile-pills {
     display: none;
-    align-items: center;
     gap: 6px;
-    padding: 8px 14px;
-    border-radius: 10px;
+    overflow-x: auto;
+    -webkit-overflow-scrolling: touch;
+    scrollbar-width: none;
+    padding-bottom: 4px;
+    margin-bottom: 12px;
+  }
+  .mobile-pills::-webkit-scrollbar { display: none; }
+
+  .pill {
+    display: flex;
+    align-items: center;
+    gap: 5px;
+    padding: 6px 12px;
+    border-radius: 999px;
     border: 1px solid rgba(35,26,17,0.1);
     background: rgba(255,252,248,0.7);
     color: #5c5046;
-    font-size: 0.82rem;
+    font-size: 0.78rem;
+    font-weight: 500;
     font-family: var(--font);
     cursor: pointer;
-    margin-bottom: 12px;
+    white-space: nowrap;
+    flex-shrink: 0;
     transition: all 160ms;
   }
-  .mobile-filter-btn:hover { background: rgba(255,248,241,0.9); color: #1e1812; }
+  .pill:hover { background: rgba(255,248,241,0.9); }
+  .pill.active {
+    background: rgba(255,248,241,0.95);
+    color: #1e1812;
+    font-weight: 600;
+    border-color: var(--pill-color, rgba(35,26,17,0.2));
+    box-shadow: inset 0 0 0 1px var(--pill-color, transparent);
+  }
+  .pill-dot {
+    width: 7px; height: 7px; border-radius: 50%; flex-shrink: 0;
+  }
+  .pill-count {
+    font-size: 0.65rem; font-family: var(--mono); color: #8c7b69;
+  }
+
+  .nav-dot {
+    width: 7px; height: 7px; border-radius: 50%; flex-shrink: 0;
+  }
 
   @media (max-width: 768px) {
-    .mobile-filter-btn { display: flex; }
+    .mobile-pills { display: flex; }
   }
 
   /* ═══ Active filter ═══ */