fix(studio-server): preserve binary bodies in file PUT/POST

[yegor177]

Problem

PUT/POST /api/projects/:id/files/* in @hyperframes/studio-server read the request body with c.req.text() and write it with writeFileSync(path, body, "utf-8"). Any body that is not valid UTF-8 — fonts, images, any binary asset — gets its non-UTF-8 bytes replaced with U+FFFD during the decode, so the file on disk is silently corrupted (and typically inflated). The Content-Type header is ignored.

Repro

curl -X PUT -H "Content-Type: application/octet-stream" \
  --data-binary @font.otf \
  http://localhost:3002/api/projects/<id>/files/assets/font.otf
# → 200, but the file on disk has a different sha256 and a larger size

Observed with a 20 828-byte OTF font arriving as 37 041 bytes on disk; @font-face then falls back silently, which makes this painful to diagnose.

Fix

Read the raw bytes (Buffer.from(await c.req.arrayBuffer())) and write the buffer without an encoding. This is byte-exact for text bodies too (UTF-8 text round-trips unchanged), so existing text uploads keep working — no content-type sniffing needed.

Testing

• Added a vitest case in files.test.ts: POST + PUT with bodies containing invalid-UTF-8 bytes round-trip byte-for-byte.
• Verified on a live studio-server deployment: sha256 of an uploaded OTF/PNG now matches the source exactly; HTML/text uploads (including non-ASCII content) unchanged.