feat(FileUploader): Add custom per-uploader file size limit

[usernane]

Problem Statement

FileUploader reads upload_max_filesize from PHP config but doesn't let you set a custom per-uploader size limit. Applications often need different size limits for different upload contexts (e.g., avatar images vs document uploads).

Proposed Solution

Add setMaxFileSize(int $sizeInBytes) and getMaxFileSizeLimit() methods. During upload, reject files exceeding the custom limit with a descriptive error.

Alternatives Considered

• Only relying on PHP's ini setting (insufficient for per-context limits)

Breaking Change

No

[usernane]

Dependency Graph

Dependencies:

• Depends on: nothing (standalone feature)
• Related: feat(FileUploader): Add upload callback hooks for logging and validation #53 (callbacks can also reject based on size)
• Related: feat(FileUploader): Streaming upload processing with hash verification #84 (streaming processor checks size before streaming)
• Blocks: test(security): Add security-focused test cases #86 (security tests validate size limits)