Reduce media bandwidth: compress uploads, add long-lived cache headers, gzip API

- Resize/re-encode every uploaded image server-side (posts, avatars, stories,
  shop products/logo, chat messages) via a shared sharp-based optimizer —
  caps dimensions to what's actually displayed and re-compresses in place,
  cutting a typical raw camera photo by ~90% with no visible quality loss
- Cap uploaded video resolution/bitrate (re-encode only when above 1280px/
  ~2.5Mbps) alongside the existing faststart step; apply faststart+cap to
  story and chat videos too (previously stored completely raw)
- Add long-lived Cache-Control to all /storage static routes so clients stop
  re-downloading unchanged media on every request
- Add gzip/brotli compression for JSON API responses (feed/explore/chat)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

utils/downloadRemoteImage.js

@@ -1,6 +1,7 @@
 const fs = require('fs-extra')
 const path = require('path')
 const axios = require('axios')
+const { optimizeImageFile } = require('./imageOptimize')
 
 const EXT_BY_CONTENT_TYPE = {
   'image/png': '.png',
@@ -32,6 +33,7 @@ async function downloadImageToProfiles(url, baseName) {
   const filePath = path.join(uploadDir, uniqueFileName)
 
   await fs.writeFile(filePath, Buffer.from(response.data))
+  await optimizeImageFile(filePath, { maxDimension: 800 })
 
   return `/profiles/${uniqueFileName}`
 }