Introduce support for configuring unlimited upload limits by allowing -1
as a valid value for anonymous and user upload MB limits.
Changes include:
- Added `envMegabytesLimitFloat` and helper functions to parse and validate limits where -1 is allowed.
- Updated validation logic to accept -1 for `AnonymousMaxUploadMB`, `AnonymousDailyUploadMB`, and `UserDailyUploadMB`.
- Added a test case to verify unlimited upload policy behavior.
- Introduce S3-compatible storage backend support using minio-go.
- Add configuration options for local storage limits, box limits, and rate limiting.
- Implement storage backend selection (local vs S3) for anonymous and registered users.
- Add an `/admin/storage` management interface.
- Update documentation and environment examples with the new configuration variables.
- Add environment variables to configure anonymous uploads, daily upload caps, and default user storage limits.
- Update config loader to parse and validate the new settings.
- Implement backend logic to track daily usage and active storage per user.
- Update README and `.env.example` to document the new settings and admin panels.
