feat: BooCode 2.0 UI — Ember theme, brand banner, coder tabs, model-attribution chips

- Ember theme (Obsidian charcoal + #ff7a18 orange), now DEFAULT_THEME_ID; server theme_id whitelist gains 'ember'
- Brand banner: transparent Westie mascot + >_BooCode wordmark, big/edge-to-edge (flood-filled to transparency + cropped)
- Coder panes are multi-tab: + opens a BooCode tab, split opens a pane (shared ChatTabBar via tabKind + createCoderTab; closeOtherTabs/tab-numbering extended to coder)
- Model-attribution: new messages.model column stamped at finalizeCompletion (BooChat/native coder) + dispatcher assistant-row creation (external coder); surfaced via view + wire types + live frame; rendered as a subtle shortened-name chip (shortenModelName)
- Composer Web toggle moved into a boxed focus-ringed input; glowing accent dot on tool rows
- Claude SDK follow-ups (1M context, follow-up-message fix, collapsed thinking/tool chips) + CLAUDE_SDK_BACKEND=1

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/components/ProjectSidebar.tsx

@@ -3,6 +3,8 @@ import { NavLink, useLocation, useNavigate } from 'react-router-dom';
 import { ChevronRight, ExternalLink, Folder, MessageSquare, Plus, Settings as SettingsIcon, X, Code } from 'lucide-react';
 import { toast } from 'sonner';
 import { Button } from '@/components/ui/button';
+import mascot from '@/assets/brand/banner-mascot.png';
+import wordmark from '@/assets/brand/banner-wordmark.png';
 import { sessionEvents } from '@/hooks/sessionEvents';
 import {
   ContextMenu,
@@ -307,9 +309,22 @@ export function ProjectSidebar() {
 
   return (
     <aside className={asideCls}>
-      <div className="px-4 py-3 border-b flex items-center justify-between">
-        <NavLink to="/" className="font-semibold tracking-tight text-base">
-          BooCode
+      <div className="px-2 py-1 border-b flex items-center justify-between gap-1">
+        {/* BooCode brand banner: mascot badge + >_BooCode wordmark, big and
+            visible, on transparent backgrounds (no chip, no blend). */}
+        <NavLink to="/" aria-label="BooCode home" className="flex items-center gap-0.5 min-w-0 flex-1">
+          <img
+            src={mascot}
+            alt=""
+            draggable={false}
+            className="h-12 w-auto select-none shrink-0"
+          />
+          <img
+            src={wordmark}
+            alt="BooCode"
+            draggable={false}
+            className="h-12 w-auto select-none min-w-0 flex-1 object-contain object-left"
+          />
         </NavLink>
         <div className="flex items-center gap-1">
           <Button size="icon-sm" variant="ghost" onClick={() => setAddOpen(true)} aria-label="Add project">