feat: detect AI disclosure in branch name

[Emirhankeles10]

Description
Adds a branchname detector that flags branches created by AI coding CLIs/agents using their conventional prefixes (codex/, claude/, cursor/, copilot/, devin/, cline/, aider/, gemini/), matching the pattern noticed in chaoss/CollectOSS#397.

• New detection.Input.BranchName field + GetBranchName() accessor
• New gitops.GetCurrentBranch(repoPath) resolving the checked-out branch once per scan (empty string, no error, on detached HEAD)
• New detection/branchname detector, registered alongside the existing detectors
• Confidence: medium (naming convention, not proof, same tier as commit-message pattern matches)

This PR fixes #50

Notes for Reviewers

• Verified locally: a repo with a commit on a codex/fix-typo branch is flagged (medium confidence), a normal feature/... branch is not.
• go test ./... and go vet ./... pass.
• Prefix list mirrors the tool names already used by the committer detector; happy to extend/adjust the prefix map if there are other conventions to cover.

Signed commits

• Yes, I signed my commits.

Generative AI disclosure

Please select one option:

• This contribution was NOT assisted or created by Generative AI tools.
• This contribution was assisted or created by Generative AI tools.

If AI tools were used, please provide details below:

• What tools were used? Claude (Claude Code)
• How were these tools used? I asked Claude Code to find a good-first-issue in an active open-source project, and it picked this issue, read the existing detectors to follow the codebase's conventions, wrote the implementation (detector, gitops helper, wiring) and the tests, and drafted this PR description.
• Did you review these outputs before submitting this PR? Yes: I watched it reproduce the current behavior first, reviewed the diff, and confirmed locally that go test ./... passes and that the CLI correctly flags a codex/* branch while leaving a normal branch untouched before opening this PR.

[omkar-foss]

PR looks good overall, could you also update the README to include this new detector?

[omkar-foss]

README changes look good to me, thank you.

[andrew]

Nice first contribution, thanks for picking this up.

A couple of non-blocking notes for follow-up (not asking for changes here):

• The branch name is resolved once and stamped on every commit in the range, so a 10-commit PR on codex/foo produces 10 identical branchname findings. Might be worth deduping at the report level or only emitting on the tip commit at some point.
• The finding is tied to whatever branch is currently checked out rather than to the commits themselves, so ScanCommit on an arbitrary hash will flag it if you happen to be sitting on a codex/* branch, and it never fires under detached HEAD (most CI checkouts). Fine for the main use case of scanning a PR from its head branch, just something to keep in mind.
• A few of the prefixes (claude/, aider/, cline/, gemini/) I'm less sure actually auto-create branches with that convention the way Codex/Cursor/Copilot/Devin do. Medium confidence covers it though, and we can trim the map later if any turn out to be noise.

[MoralCode]

I know I'm late to the party but it looks like this first contribution went smoothly, so congrats!

I'd love to invite you to join the CHAOSS Slack in the #data-ai-disclosure-detection channel if youre interested in chatting with us more or getting help finding your next contribution