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/Workspace.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useMemo, useState } from 'react';
-import { Terminal, Code, Clipboard } from 'lucide-react';
+import { Terminal, Clipboard } from 'lucide-react';
 import { api } from '@/api/client';
 import type { Chat, Project, Session, WorkspacePane } from '@/api/types';
 import { MAX_PANES, activePaneChatId, type UseWorkspacePanesResult } from '@/hooks/useWorkspacePanes';
@@ -60,6 +60,7 @@ export function Workspace({
     closeAllTabs,
     showLandingPage,
     addSplitPane,
+    createCoderTab,
     removePane,
     reopenPane,
     hasClosedPanes,
@@ -214,18 +215,27 @@ export function Workspace({
                   onRemovePane={panes.length > 1 ? () => removePane(idx) : undefined}
                 />
               )}
+              {/* Coder panes host BooCode tabs (one chat = one agent context,
+                  all sharing the session worktree). "+" adds a tab; the split
+                  button adds a pane. Same tab strip as chat panes (tabKind). */}
               {isCoder && !isMobile && (
-                <div className="flex items-center gap-1 border-b border-border px-2 py-1 shrink-0">
-                  <Code size={12} className="text-muted-foreground" />
-                  <span className="text-xs text-muted-foreground">BooCode</span>
-                  <PaneHeaderActions
-                    className="ml-auto"
-                    onSplitPane={onAddPane}
-                    onReopenPane={hasClosedPanes ? reopenPane : undefined}
-                    onShowHistory={() => showLandingPage(idx)}
-                    onRemovePane={panes.length > 1 ? () => removePane(idx) : undefined}
-                  />
-                </div>
+                <ChatTabBar
+                  pane={pane}
+                  tabs={chatsForPane(pane)}
+                  tabKind="coder"
+                  tabNumbers={tabNumbers}
+                  onSwitchTab={(tabIdx) => switchTab(idx, tabIdx)}
+                  onRemoveTab={(chatId) => removeTab(idx, chatId)}
+                  onCloseOthers={(chatId) => closeOtherTabs(idx, chatId)}
+                  onCloseToRight={(chatId) => closeTabsToRight(idx, chatId)}
+                  onCloseAll={() => closeAllTabs(idx)}
+                  onNewTab={() => void createCoderTab(idx)}
+                  onSplitPane={(kind) => onAddPane(kind)}
+                  onReopenPane={hasClosedPanes ? reopenPane : undefined}
+                  onShowHistory={() => showLandingPage(idx)}
+                  onRename={renameChat}
+                  onRemovePane={panes.length > 1 ? () => removePane(idx) : undefined}
+                />
               )}
               {isTerminal && (
                 <div className="flex items-center gap-2 border-b border-border bg-muted/30 px-2 py-1 shrink-0">