Fix Next.js 16 upgrade issues and local media rendering

[mikecebul]

Summary

• Upgrade the app to Next.js 16 and refresh related config, lockfile, and generated files
• Replace deprecated Next ESLint config usage with a flat ESLint setup
• Update revalidation hooks to the current Next cache API so build and typecheck succeed
• Normalize local media URL handling to avoid private-IP and local pattern issues while preserving external R2 URLs
• Refine hero and two-column image/corner-dot rendering to stabilize desktop layout and carousel decoration placement
• Update docs and env examples to use DATABASE_URI

Testing

• pnpm typecheck
• pnpm lint