Replace axios with fetch in frontend request paths

[Copilot]

This PR removes axios from the client bundle and migrates existing request callsites to native fetch. The goal is to keep current request/response behavior while dropping the extra dependency.

• Request client migration

  • Replaced Axios.put(...) in AsyncCheckbox with fetch (PUT, FormData, same-origin credentials, X-Requested-With header).
  • Replaced Axios.post(...) in Upload with fetch (POST, FormData, same request headers/credentials).

• Behavior compatibility

  • Kept upload response handling aligned with existing code by returning { data: ... }-shaped results from the new fetch path.
  • Preserved existing upload error surface by mapping request failures into the current per-file errors structure.

• Failure handling improvements

  • Added explicit non-2xx status checks with actionable error messages.
  • For async checkbox updates, request failure now reverts the toggled value and reports an inline validity error to the user.

• Dependency cleanup

  • Removed axios from package.json and regenerated yarn.lock.

// Before
Axios.put(uri, data)

// After
fetch(uri, {
  method: 'PUT',
  headers: { 'X-Requested-With': 'XMLHttpRequest' },
  body: data,
  credentials: 'same-origin'
})