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/server/src/routes/settings.ts

@@ -22,8 +22,9 @@ export async function setSetting(
   `;
 }
 
-// themes-v1: whitelist of the 18 preset theme ids. Kept in sync with
+// themes-v1: whitelist of the preset theme ids. Kept in sync with
 // docs/themes_v1.md §1 and apps/web/src/lib/theme.ts THEMES.
+// (+ 'ember' — the BooCode 2.0 signature, now the default.)
 const THEME_IDS = [
   'obsidian',
   'gunmetal',
@@ -43,6 +44,7 @@ const THEME_IDS = [
   'chalk',
   'cobalt',
   'midnight-sapphire',
+  'ember',
 ] as const;
 
 const THEME_MODES = ['dark', 'light', 'system'] as const;