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/ContextBar.tsx

@@ -19,18 +19,24 @@ interface Props {
 // the same boundaries the server's auto-compaction triggers.
 const COMPACTION_BUFFER = 20_000;
 
-// Walk newest-first; first message with both ctx_used and ctx_max non-null
-// AND ctx_max > 0 wins. Older messages may have ctx_used but missing ctx_max
-// (early v1 before llama-swap's n_ctx capture worked) — skip them and keep
-// walking. Returns null when no usable pair exists in the chat.
+// Take the latest ctx_used and the latest ctx_max INDEPENDENTLY (newest-first).
+// They needn't be on the same message: ctx_max is the model's context window — a
+// constant per model — while some agents report it only intermittently (the claude
+// SDK populates modelUsage.contextWindow on some turns, not all) yet report
+// ctx_used every turn. Pairing the latest of each gives a correct used/max even
+// when the most recent turn omitted the window. Native BooChat sets both on the
+// same assistant message, so this is identical there. Returns null until BOTH a
+// used and a positive max have been seen at least once.
 function latestPair(messages: Message[]): { used: number; max: number } | null {
+  let used: number | null = null;
+  let max: number | null = null;
   for (let i = messages.length - 1; i >= 0; i--) {
     const m = messages[i]!;
-    if (m.ctx_used == null || m.ctx_max == null) continue;
-    if (m.ctx_max <= 0) continue;
-    return { used: m.ctx_used, max: m.ctx_max };
+    if (used === null && m.ctx_used != null) used = m.ctx_used;
+    if (max === null && m.ctx_max != null && m.ctx_max > 0) max = m.ctx_max;
+    if (used !== null && max !== null) break;
   }
-  return null;
+  return used !== null && max !== null ? { used, max } : null;
 }
 
 interface ColorTier {