#3430 swamp-club.com serves every response uncompressed

Production sends no Content-Encoding on any response, even when the client sends Accept-Encoding: gzip, br. Measured against swamp-club.com:

• / HTML: 31.7KB uncompressed today. The new homepage is about 187KB, or about 46KB gzipped.
• /assets/client-entry-*.css: 183KB uncompressed, cached immutable, but never compressed.
• /assets/*.js modulepreloads: uncompressed, and served Cache-Control: no-cache, no-store because the preload URLs carry no __frsh_c build param. Returning visitors download them again on every page view.

Cause: deno serve on 2.9.6 does not compress on its own (checked with a minimal deno serve handler: no Content-Encoding), and nothing in front of the app compresses.

Fix options:

1. An outermost app.use in main.ts, ahead of staticFiles() so assets are covered. It would gzip compressible types through CompressionStream; skip text/event-stream (/api/v1/lab/stream), HEAD, 1xx/204/206, existing Content-Encoding, and no-transform; drop Content-Length; add Vary: Accept-Encoding.
2. Fix the no-store on hashed JS assets separately. Those file names are content-hashed, so they can be immutable.