Resolve repository TODOs and fill missing test coverage

[arnavk23]

No description provided.

[Copilot]

Pull request overview

This PR resolves TODO comments throughout the codebase and adds missing test coverage. The changes improve code quality by replacing placeholder TODOs with actual implementations or clarifying comments, and by adding test assertions to verify expected behavior.

Changes:

• Resolved TODOs in test files by adding missing test coverage for InvalidProject exception handling and adding mock verification assertions
• Updated HTML templates to include actual header and footer content instead of TODO placeholders
• Clarified comments in repo.py regarding datetime usage, PyGithub compatibility, and Git version compatibility on Debian
• Removed TODO comment in publish.py related to prerelease support

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/action/test_repo.py	Added test for InvalidProject exception in is_registered() method; removed redundant case-insensitive URL test
test/action/test_changelog.py	Added mock verification assertions to test_collect_data() to ensure all expected methods are called
tagbot/web/templates/base.html	Added header with "TagBot" title and footer with source link, replacing TODO placeholders
tagbot/action/repo.py	Updated comments for clarity: changed datetime TODO to use datetime.utcnow(), clarified PyGithub compatibility comment, refined Debian Git version comment
bin/publish.py	Removed TODO comment about prerelease support

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