#3616 Dev server (Vite) sends HTML pages with content-encoding: gzip over a body that isn't gzip

Under docker compose up app (deno task dev, Vite HMR), every HTML page answers content-encoding: gzip with a body that is not gzip. Static files are fine.

Repro on main (cbd6f2b-era, includes #1359 'gzip responses again'):

• curl -s --compressed http://127.0.0.1:8000/extensions → exit 61, 0 bytes (same for /, /manual, an extension page)
• curl -s -H 'Accept-Encoding: gzip' http://127.0.0.1:8000/ | file - → 'data', not gzip
• /robots.txt with the same header is valid gzip
• Chromium (Playwright) never fires domcontentloaded on these pages, so local Playwright verification of any page hangs
• Production is fine: curl --compressed https://swamp-club.com/extensions → 200, 46 KB

Likely the gzip in deliverResponse (main.ts / lib/http-compression.ts) interacting with Vite's dev middleware for HTML (double handling, or the encoding header kept after the body was replaced). Found while verifying swamp-club#3353; unrelated to that change.