feat(opennext): experimental opennext/workers support

[theuargb]

Adds a Cloudflare Workers/OpenNext deployment path while keeping the existing Node deployment path usable.

What Changed

• Added OpenNext Cloudflare config, Wrangler config, worker build/deploy scripts, static asset headers, and local worker env example.
• Upgraded Next to 16.2.10 to match current @opennextjs/cloudflare support.
• Added Hyperdrive-aware Postgres connection handling for Workers.
• Added pg-cloudflare and tracing config so pg bundles correctly for Workers.
• Kept normal Node storage options, but forces Workers to use S3-compatible storage for R2.
• Updated S3 storage download handling for both Node streams and Worker/Web stream bodies.
• Preserved stdio/file-based MCP for Node deployments, while Workers automatically use remote-only MCP and hide/reject stdio configs.
• Moved the auth gate from Next 16 proxy.ts to middleware.ts because OpenNext Cloudflare cannot run Node proxy yet.
• Skips startup migrations and eager MCP init on Workers; Node behavior remains.
• Added guards for Node-only APIs like process.on() and timer .unref().

Notes

Worker deploy still needs real Cloudflare values:

• Replace Hyperdrive ID in wrangler.jsonc.
• Configure R2 S3 API env/secrets.
• Set production auth/base URL secrets.

[vercel]

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[theuargb]

now requires #383