Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

• Added a Filename pattern preference in settings to allow custom filename patterns. This works similarly to automatic backups in Fossify Calendar and others.
• Grouped audio-related preferences in a new Audio category.

Tests performed

• Custom filenames working for all formats
• Empty patterns are not allowed
• Patterns without a datetime placeholders are not allowed

Before & after preview

Closes the following issue(s)

• Closes Feature: Option for alternative (more readable) filename patterns #15

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.