docs: document storage upload HTTP API for edge functions

[MajorTal]

Problem

The CLI docs show run402 storage upload but don't document the HTTP API for uploading from an edge function. Had to guess the URL pattern and auth header.

Suggested Solution

Add to the storage section or functions section:

// Upload from an edge function
const res = await fetch('https://api.run402.com/storage/v1/upload/my-bucket/path/file.pdf', {
  method: 'POST',
  headers: { Authorization: 'Bearer ' + process.env.RUN402_SERVICE_KEY },
  body: fileBuffer,
});