refactor(dav): modernize TagsPlugin with strict types and improved logic

[joshtrichards]

• Resolves: #

Summary

• Use strict types throughout TagsPlugin
• Switch to typed properties and constructor parameters
• Improve tag and favorite logic for robustness and readability
• Rewrite/add documentation blocks for clarity
• Reformat code, reorganize methods for maintainability
• Remove dead code and outdated patterns

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)