feat: add changelog and versioning, surface it in admin

Bumps version to 0.2.0 (root + apps/web package.json) and adds
CHANGELOG.md as the canonical human-readable history, mirrored by
apps/web/lib/changelog.ts as the in-app data source (single
ChangelogList component renders both).

- /changelog: user-facing page, linked from the account dropdown.
- /admin/changelog: same list, plus a "Version" card on the admin
  overview dashboard linking to it.

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

apps/web/app/(app)/changelog/page.tsx

@@ -0,0 +1,19 @@
+import type { Metadata } from "next";
+import { ChangelogList } from "@/components/shared/changelog-list";
+import { APP_VERSION } from "@/lib/changelog";
+
+export const metadata: Metadata = {};
+
+export default function ChangelogPage() {
+  return (
+    <div className="space-y-2">
+      <div>
+        <h1 className="text-3xl font-bold tracking-tight">Changelog</h1>
+        <p className="text-muted-foreground mt-1">Currently running v{APP_VERSION}.</p>
+      </div>
+      <div className="pt-4">
+        <ChangelogList />
+      </div>
+    </div>
+  );
+}