fix(proxy): preserve binary request bodies and forward DELETE/OPTIONS bodies (#157)

[Baddevil512]

/claim #157
Closes #157

Problem

/proxy previously decoded request bodies as UTF-8 text (req.clone().text()), corrupting binary payloads by replacing invalid UTF-8 sequences with replacement bytes (0xef 0xbf 0xbd). In addition, DELETE and OPTIONS request bodies were dropped.

Fix

1. Updated routes/proxy.ts to extract request bodies as raw ArrayBuffer (await req.clone().arrayBuffer()) for all HTTP methods except GET and HEAD when rawBody.byteLength > 0.
2. Added regression tests in tests/routes/proxy-binary-body.test.ts verifying byte-for-byte binary payload preservation (Uint8Array([0x00, 0xff, 0xfe, 0x80, 0x41])) across POST, PUT, PATCH, DELETE, and OPTIONS requests while keeping empty OPTIONS preflights clean.

Verification

• bun test: 34 pass, 0 fail (180 expect() calls)
• bunx tsc --noEmit: 0 errors
• bun biome format: 0 errors