Problem

PDD Cloud needs to run the same full checkup used at the end of pdd-issue when a user labels a pull request with pdd-checkup.

Today the full path requires both:

pdd checkup --pr <pr-url> --issue <issue-url> --final-gate

That blocks PR-only checkup for PRs that do not have a linked issue.

Expected behavior

Allow this command:

pdd checkup --pr https://github.com/org/repo/pull/123 --final-gate

In this mode, final-gate should run the full PR readiness check against the PR itself and skip issue-alignment checks because no source issue was supplied.

If --issue is supplied, keep the current issue-alignment behavior unchanged.

Acceptance criteria

• pdd checkup --pr <pr-url> --final-gate is accepted without --issue.
• The PR worktree/final-gate/review-loop behavior still runs.
• Issue-alignment gates are skipped only when --issue is absent.
• Existing --pr <pr-url> --issue <issue-url> --final-gate behavior is unchanged.
• Add tests for final-gate with and without --issue.