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/styles/globals.css

@@ -25,6 +25,7 @@
 @import "./themes/chalk.css";
 @import "./themes/cobalt.css";
 @import "./themes/midnight-sapphire.css";
+@import "./themes/ember.css";
 
 @custom-variant dark (&:is(.dark *));
 

apps/web/src/styles/themes/ember.css

@@ -0,0 +1,76 @@
+/* BooCode Ember (family: Amber) — the signature brand theme. Mirrors the
+   Obsidian theme's flat charcoal structure (same neutrals, flat hairline
+   borders), with ember orange (--accent #ff7a18) swapped in for Obsidian's
+   purple. Dark anchors: #0c0c0e #15151a #1f1f23 #6b6b75 #ff7a18. */
+.theme-ember {
+  --background: #fafafa;
+  --foreground: #18181b;
+  --card: #f4f4f5;
+  --card-foreground: #18181b;
+  --popover: #f4f4f5;
+  --popover-foreground: #18181b;
+  --primary: #e25f00;
+  --primary-foreground: #ffffff;
+  --secondary: #e4e4e7;
+  --secondary-foreground: #18181b;
+  --muted: #e4e4e7;
+  --muted-foreground: #71717a;
+  --accent: #e25f00;
+  --accent-foreground: #ffffff;
+  --destructive: #b91c1c;
+  --destructive-foreground: #ffffff;
+  --border: #e4e4e7;
+  --input: #e4e4e7;
+  --ring: #e25f00;
+  --sidebar: #f4f4f5;
+  --sidebar-foreground: #18181b;
+  --sidebar-primary: #e25f00;
+  --sidebar-primary-foreground: #ffffff;
+  --sidebar-accent: #e4e4e7;
+  --sidebar-accent-foreground: #18181b;
+  --sidebar-border: #e4e4e7;
+  --sidebar-ring: #e25f00;
+}
+.theme-ember.dark {
+  --background: #0c0c0e;
+  --foreground: #ece9f0;
+  --card: #15151a;
+  --card-foreground: #ece9f0;
+  --popover: #15151a;
+  --popover-foreground: #ece9f0;
+  --primary: #ff7a18;
+  --primary-foreground: #120a04;
+  --secondary: #1f1f23;
+  --secondary-foreground: #ece9f0;
+  --muted: #1f1f23;
+  --muted-foreground: #6b6b75;
+  --accent: #ff7a18;
+  --accent-foreground: #120a04;
+  --destructive: #dc2626;
+  --destructive-foreground: #ffffff;
+  --border: #1f1f23;
+  --input: #1f1f23;
+  --ring: #ff7a18;
+  --sidebar: #15151a;
+  --sidebar-foreground: #ece9f0;
+  --sidebar-primary: #ff7a18;
+  --sidebar-primary-foreground: #120a04;
+  /* Softened selected/hover surface — a faint accent tint, NOT the solid bright
+     accent Obsidian uses (per your earlier "selected button shouldn't be solid
+     orange"). Set --sidebar-accent: #ff7a18 + foreground #120a04 for parity. */
+  --sidebar-accent: color-mix(in oklab, #ff7a18 16%, transparent);
+  --sidebar-accent-foreground: #ece9f0;
+  --sidebar-border: #1f1f23;
+  --sidebar-ring: #ff7a18;
+}
+
+/* User message bubble: a dark surface card with a 2px accent right-edge — not
+   the solid-orange fill (per your earlier preference). Remove this block to get
+   the Obsidian-style solid-accent bubble. */
+.theme-ember.dark .boo-user-bubble {
+  background: var(--popover);
+  color: var(--foreground);
+  border: 1px solid var(--border);
+  border-right: 2px solid var(--primary);
+  border-radius: 6px;
+}