Describe the bug
Submitty currently treats any file that begins with . as a metadata file.

This behavior hides legitimate student files from the Submitted Files panel and excludes them from normal submission file handling.

For example, if a student uploads a file named .hidden or .txt, Submitty classifies it as a metadata file even though it is a user submitted file.

Only Submitty generated metadata files should receive special handling.

Expected behavior
Submitty should only classify known Submitty metadata files as metadata.

Examples include:

.submit.timestamp
.submit.notebook
.submit.VCS_CHECKOUT
.user_assignment_access.json

Student uploaded files that begin with . should remain visible and behave like normal submission files.

To Reproduce

1. Create a gradeable that accepts file uploads.
2. Submit a file named .hidden.
3. View the submission as the student or instructor.
4. Observe that the file does not appear in the Submitted Files panel.

Configuration
OS: Ubuntu 22.04 (Vagrant development VM)
Browser: Chrome

Screenshots
Student side:

Blank upload shown.

Instructor side:

Additional context
The issue appears to originate from logic in AutoGradedVersion::loadSubmissionFiles().

Current behavior classifies files as metadata based solely on whether the filename begins with ..

This causes user submitted dotfiles to be treated the same as Submitty generated metadata files.