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/PaneHeaderActions.tsx

@@ -12,10 +12,14 @@ import { cn } from '@/lib/utils';
 // desktop coder + terminal pane headers (Workspace) so all pane kinds share one
 // control set. Extracted to avoid a divergent copy per header.
 interface Props {
-  // When provided (chat panes), the "+" menu's New BooChat opens an in-pane
-  // tab. When omitted (coder/terminal panes, which can't host tabs), New BooChat
-  // splits into a new pane instead.
+  // When provided, the "+" menu item matching `tabKind` opens an in-pane tab
+  // (e.g. chat panes: New BooChat → tab; coder panes: New BooCode → tab). Every
+  // OTHER kind splits into a new pane. When onNewTab is omitted (terminal
+  // panes, which can't host tabs) all three items split.
   onNewTab?: () => void;
+  // The host pane's own kind — the "+" item of this kind becomes "new tab".
+  // Defaults to 'chat' for back-compat with the chat tab bar.
+  tabKind?: 'chat' | 'terminal' | 'coder';
   onSplitPane: (kind: 'chat' | 'terminal' | 'coder') => void;
   onReopenPane?: () => void;
   onShowHistory: () => void;
@@ -31,6 +35,7 @@ const BTN =
 
 export function PaneHeaderActions({
   onNewTab,
+  tabKind = 'chat',
   onSplitPane,
   onReopenPane,
   onShowHistory,
@@ -38,6 +43,10 @@ export function PaneHeaderActions({
   historyActive,
   className,
 }: Props) {
+  // The "+" item of the host pane's own kind adds a tab; every other kind
+  // splits into a new pane. Falls back to split when onNewTab is absent.
+  const newOrSplit = (kind: 'chat' | 'terminal' | 'coder') =>
+    onNewTab && tabKind === kind ? onNewTab : () => onSplitPane(kind);
   return (
     <div className={cn('flex items-center gap-0.5 shrink-0', className)}>
       <DropdownMenu>
@@ -53,15 +62,15 @@ export function PaneHeaderActions({
           </button>
         </DropdownMenuTrigger>
         <DropdownMenuContent align="end" className="w-fit">
-          {/* Chat panes: New BooChat opens a tab in THIS pane. Coder/terminal
-              panes can't host tabs, so it splits into a new pane. */}
-          <DropdownMenuItem onSelect={onNewTab ?? (() => onSplitPane('chat'))}>
+          {/* The item matching the host pane's kind opens an in-pane tab; the
+              others split into a new pane. (tabKind defaults to 'chat'.) */}
+          <DropdownMenuItem onSelect={newOrSplit('chat')}>
             <MessageSquare size={14} /> New BooChat
           </DropdownMenuItem>
-          <DropdownMenuItem onSelect={() => onSplitPane('terminal')}>
+          <DropdownMenuItem onSelect={newOrSplit('terminal')}>
             <Terminal size={14} /> New BooTerm
           </DropdownMenuItem>
-          <DropdownMenuItem onSelect={() => onSplitPane('coder')}>
+          <DropdownMenuItem onSelect={newOrSplit('coder')}>
             <Code size={14} /> New BooCode
           </DropdownMenuItem>
         </DropdownMenuContent>