Chat layout: history in the main sidebar, consistent header, cleaner icon

- Desktop: on /chat the main sidebar shows the chat list (search, New chat,
  items with rename/delete, active highlight) in place of the deck
  navigation; the separate second column is gone and the chat uses the full
  width. The expand/collapse chevron sits outside the swappable section and
  a collapsed rail stays clean (the highlighted Chat row already opens a
  new chat). Active conversation travels via a tiny store (lib/chat-active)
  so the sidebar needs no useSearchParams and pages stay static.
- Header (phones): history, theme and New chat are now identical chips -
  same 44px hit area, rounded-2xl, border/surface tokens, size-5 icons,
  even spacing; the title block truncates cleanly. ThemeToggle gained a
  'plain' variant so the header styles it without touching other pages.
- ChatIcon redrawn (clean message-circle, no inner lines) and the empty
  state uses the app's icon-chip pattern (size-12 chip, accent-600/200)
  instead of the bare oversized glyph; the model chip icon follows.
- Also fixed a pre-existing dev-only breakage found while verifying: the
  tab-bar bounce animated three keyframes with a spring, which framer
  motion's dev build throws on - breaking client updates in the dev
  instance (library tab switching, sheet Escape). It now uses a tween.
- Dev metadata keeps the Apple icons in both branches.
- SW -> freezmo-v35.

lib/chat-active.ts

@@ -0,0 +1,29 @@
+"use client";
+
+/**
+ * Which conversation the chat screen is currently showing, for surfaces
+ * outside the chat route (the sidebar list highlights it). A tiny external
+ * store instead of reading `?c=` from the URL, because the sidebar renders on
+ * every page and `useSearchParams` there would force pages dynamic.
+ */
+
+let active: string | null = null;
+const listeners = new Set<() => void>();
+
+export const chatActive = {
+  set(id: string | null): void {
+    if (active === id) return;
+    active = id;
+    listeners.forEach((listener) => listener());
+  },
+  subscribe(listener: () => void): () => void {
+    listeners.add(listener);
+    return () => listeners.delete(listener);
+  },
+  getSnapshot(): string | null {
+    return active;
+  },
+  getServerSnapshot(): string | null {
+    return null;
+  },
+};