fix(specgit): reject title types unsupported by branch ruleset

[LeXwDeX]

This was generated by AI during triage.

Why

SpecGit accepts issue title types such as ci: and derives a ci/** branch, but this repository's branch-naming ruleset allows only feat, fix, chore, docs, refactor, test, release, and hotfix. During #519 the remote push was rejected by GH013 only after tracker and local delivery state had already been created.

Scope

• Add a repository-local preflight that validates the requested issue type against the branch-prefix allowlist before SpecGit performs remote side effects.
• Report the allowed type vocabulary and the corrected command.
• Do not silently map one semantic type to another.

Out of scope: weakening the GitHub branch-naming ruleset.

Acceptance

• ci: and any other unsupported type fail locally before issue, branch, push, or PR creation.
• Every allowed prefix passes the preflight and retains its original type.
• The allowlist has one documented source of truth shared with the bootstrap wrapper.

Dependency

• Blocked by chore(specgit): automate bootstrap around required harness specializations #521's safe repository-local bootstrap seam.

[LeXwDeX]

This was generated by AI during triage.

Agent brief: the issue body is the verified delivery contract. Implement only after #521 provides the safe repository-local bootstrap seam; preserve all branch rulesets and SpecGit acceptance gates.

[LeXwDeX]

SpecGit delivery branch: feat/529-specgit-branch-type-preflight (draft pull request #534).

[github-actions]

Auto-closed: delivery PR #534 (view) merged into dev with a closing keyword for #529 in its body. GitHub's native auto-close only fires on the default branch (main); this mirrors it for the dev integration layer (#519).