feat: fullscreen toggle for cooking assistant and recipe chat

Both chat panels were locked to a fixed 420px slide-over with no way
to get more room for longer conversations. Adds an expand/collapse
button in the header that grows the sheet to fill the viewport.

v0.38.0

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.37.0";
+export const APP_VERSION = "0.38.0";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.38.0",
+    date: "2026-07-17 13:00",
+    added: [
+      "The cooking assistant and per-recipe chat can now expand to fullscreen — a new toggle in the chat header.",
+    ],
+  },
   {
     version: "0.37.0",
     date: "2026-07-17 12:30",