Release Notes: v1.9.0

feat: implement dedicated changelog, GitHub release integration, and streamline profile UX

• Remove redundant /login route; integrate anonymous authentication flow directly into /profile to eliminate confusing redirects.
• Add GitHub API integration (src/lib/github.ts) to fetch releases.
• Implement /api/releases route handler with Edge caching (revalidate = 1800) for zero-cost server fetching.
• Create a dedicated /changelog page displaying an accordion of full release notes.
• Build WhatsNewModal and Changelog UI components with custom Markdown parser.
• Wrap application with WhatsNewProvider for global release alerts.
• Update SettingsPage to surface only the latest release snippet.
• Resolve hydration mismatch in RootLayout by explicitly identifying the inline theme script.
• Update Footer and sitemap.ts to reflect route structure changes.

Full Changelog: v1.8.1...v1.9.0