feat: ChatGPT/Claude-style persistent sidebar for desktop fullscreen chat (v0.57.0)

Cooking assistant's fullscreen mode gets a real left sidebar (always-
visible conversation list, hover-reveal rename/delete) on desktop
(md+), replacing the small dropdown menu that made sense in the narrow
420px drawer but not in a full-viewport layout. Mobile fullscreen and
the normal drawer keep the dropdown (ConversationMenu) — no room for a
persistent sidebar there.

Extracted the shared fetch/rename/delete/create logic into
use-conversation-list.ts so the dropdown (ConversationMenu) and the new
sidebar (ConversationSidebar) can't silently diverge — both are thin
render layers over the same hook. ConversationMenu gained an optional
className prop so the panel can hide it with `md:hidden` specifically
when the sidebar is already covering that job.

Per-recipe chat is untouched — it's single-threaded by design and never
used either of these components.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.56.0";
+export const APP_VERSION = "0.57.0";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.57.0",
+    date: "2026-07-20 09:20",
+    added: [
+      "Cooking assistant, fullscreen on desktop, now has a persistent conversation sidebar on the left (like ChatGPT/Claude) instead of a dropdown menu — switch chats without leaving the conversation you're reading. Mobile and the normal drawer view keep the dropdown, since there's no room for a sidebar there.",
+    ],
+  },
   {
     version: "0.56.0",
     date: "2026-07-20 09:10",