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/MessageBubble.tsx

@@ -6,6 +6,7 @@ import type { Chat, ErrorReason, Message } from '@/api/types';
 import { api } from '@/api/client';
 import { sessionEvents } from '@/hooks/sessionEvents';
 import { sendToTerminal, terminalsRegistry, type TerminalRegistration } from '@/lib/events';
+import { shortenModelName } from '@/lib/modelName';
 import { CapHitSentinel } from './CapHitSentinel';
 import { DoomLoopSentinel } from './DoomLoopSentinel';
 import { MarkdownRenderer } from './MarkdownRenderer';
@@ -608,12 +609,12 @@ function SummaryCard({ message }: { message: Message }) {
 
 // Collapsible "Thinking" block for assistant reasoning. Fed by either
 // reasoning_text (coder wire / live reasoning_delta stream) or reasoning_parts
-// (native inference, persisted from message_parts). Auto-expands while the turn
-// is still streaming so the user watches it think (Paseo-style), then stays
-// where the user left it once the turn completes — initial state is captured
-// once at mount, so we never fight a manual collapse on later re-renders.
+// (native inference, persisted from message_parts). Starts COLLAPSED to start
+// (a quiet chip) — for native BooChat/BooCode and the external agents (opencode,
+// claude SDK) alike — so the transcript stays tidy; click to expand. The
+// `streaming` pulse still animates while the turn runs.
 function ReasoningBlock({ text, streaming }: { text: string; streaming: boolean }) {
-  const [expanded, setExpanded] = useState(() => streaming);
+  const [expanded, setExpanded] = useState(false);
   return (
     <div className="max-w-[90%] rounded-lg border bg-muted/30 text-sm">
       <button
@@ -768,7 +769,7 @@ export function MessageBubble({
     return (
       <div className="group flex flex-col items-end gap-1">
         <SendToTerminalMenu>
-          <div className="max-w-[80%] rounded-lg bg-primary text-primary-foreground px-3 py-2 text-sm whitespace-pre-wrap break-words min-w-0">
+          <div className="boo-user-bubble max-w-[80%] rounded-lg bg-primary text-primary-foreground px-3 py-2 text-sm whitespace-pre-wrap break-words min-w-0">
             {message.content}
           </div>
         </SendToTerminalMenu>
@@ -782,6 +783,8 @@ export function MessageBubble({
   // v1.13.7: match the MessageList.flatten trim guard so a whitespace-only
   // assistant turn doesn't render an empty bubble + dangling ActionRow.
   const hasContent = message.content.trim().length > 0;
+  // model-attribution chip: short label for the model that produced this turn.
+  const modelLabel = shortenModelName(message.model);
   // Reasoning arrives as a pre-joined string (coder wire) or as parts (native
   // inference). Read whichever is present; loose ?? chain tolerates the coder
   // shape where reasoning_parts is undefined (see CLAUDE.md null-guard note).
@@ -823,6 +826,14 @@ export function MessageBubble({
           )}
         </div>
       )}
+      {!isStreaming && (modelLabel || null) && (
+        <span
+          className="inline-flex w-fit items-center rounded-full border border-primary/25 bg-primary/10 px-2 py-0.5 text-[10px] font-mono text-primary/90"
+          title={message.model ?? undefined}
+        >
+          {modelLabel}
+        </span>
+      )}
       {!isStreaming && <StatsLine message={message} />}
       {!isStreaming && hasContent && (
         <ActionRow