fix: verify polecat branch pushed before cleanup (gt-gl6s)

Add BranchPushedToRemote() to git package that properly handles
polecat branches without upstream tracking. Update verifyPolecatState
in witness to check that branches are pushed before allowing cleanup.

This prevents the scenario where polecats close issues without pushing
their work, causing all commits to be lost when the worktree is deleted.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/git/git.go

@@ -639,3 +639,49 @@ func (g *Git) CheckUncommittedWork() (*UncommittedWorkStatus, error) {
 
 	return status, nil
 }
+
+// BranchPushedToRemote checks if a branch has been pushed to the remote.
+// Returns (pushed bool, unpushedCount int, err).
+// This handles polecat branches that don't have upstream tracking configured.
+func (g *Git) BranchPushedToRemote(localBranch, remote string) (bool, int, error) {
+	remoteBranch := remote + "/" + localBranch
+
+	// First check if the remote branch exists
+	exists, err := g.RemoteBranchExists(remote, localBranch)
+	if err != nil {
+		return false, 0, fmt.Errorf("checking remote branch: %w", err)
+	}
+
+	if !exists {
+		// Remote branch doesn't exist - count commits since origin/main (or HEAD if that fails)
+		count, err := g.run("rev-list", "--count", "origin/main..HEAD")
+		if err != nil {
+			// Fallback: just count all commits on HEAD
+			count, err = g.run("rev-list", "--count", "HEAD")
+			if err != nil {
+				return false, 0, fmt.Errorf("counting commits: %w", err)
+			}
+		}
+		var n int
+		_, err = fmt.Sscanf(count, "%d", &n)
+		if err != nil {
+			return false, 0, fmt.Errorf("parsing commit count: %w", err)
+		}
+		// If there are any commits since main, branch is not pushed
+		return n == 0, n, nil
+	}
+
+	// Remote branch exists - check if local is ahead
+	count, err := g.run("rev-list", "--count", remoteBranch+"..HEAD")
+	if err != nil {
+		return false, 0, fmt.Errorf("counting unpushed commits: %w", err)
+	}
+
+	var n int
+	_, err = fmt.Sscanf(count, "%d", &n)
+	if err != nil {
+		return false, 0, fmt.Errorf("parsing unpushed count: %w", err)
+	}
+
+	return n == 0, n, nil
+}