[codex] raise upload limit and inline safe code reloader

[puppe1990]

What changed

This PR contains two isolated commits:

1. Raise the direct upload file size limit from 2 GB to 5 GB, and update the frontend/controller/gettext messaging to reflect the configured limit.
2. Inline the safe code reloader behavior into OpenDriveWeb.Endpoint, removing the dedicated wrapper module and keeping the existing guard/test coverage.

Why

Large uploads were being rejected by the direct upload preparation step once the selected file exceeded 2_000_000_000 bytes. In practice that can also affect files that appear as roughly 1.9 GB in the UI because the browser display rounds values while the server validates exact bytes.

The code reloader change reduces indirection by keeping endpoint-specific plug behavior in the endpoint module itself.

Impact

Users can now upload files up to 5 GB through the direct upload flow.
The upload error messaging now reflects the effective configured limit instead of a hardcoded 2 GB string.
The development endpoint keeps the same guarded code reload behavior with one less module to maintain.

Validation

• mix test test/open_drive/drive_test.exs test/open_drive_web/controllers/direct_upload_controller_test.exs test/open_drive_web/safe_code_reloader_test.exs

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