feat: Add gt done command for polecat work submission

Add `gt done` command as a convenience wrapper for polecats to signal
their work is ready for the merge queue. This addresses the missing
command referenced in polecat docs.

The command:
- Submits current branch to merge queue (same as gt mq submit)
- Auto-detects issue ID from branch name (polecat/<worker>/<issue>)
- Auto-detects integration branch if source issue has epic parent
- Provides polecat-friendly output messaging

Closes gt-qna4.

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

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

internal/cmd/done.go

@@ -0,0 +1,151 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/beads"
+	"github.com/steveyegge/gastown/internal/git"
+	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+var doneCmd = &cobra.Command{
+	Use:   "done",
+	Short: "Signal work ready for merge queue",
+	Long: `Signal that your work is complete and ready for the merge queue.
+
+This is a convenience command for polecats that:
+1. Submits the current branch to the merge queue
+2. Auto-detects issue ID from branch name
+
+Equivalent to: gt mq submit
+
+Examples:
+  gt done                  # Submit current branch
+  gt done --issue gt-abc   # Explicit issue ID`,
+	RunE: runDone,
+}
+
+var (
+	doneIssue    string
+	donePriority int
+)
+
+func init() {
+	doneCmd.Flags().StringVar(&doneIssue, "issue", "", "Source issue ID (default: parse from branch name)")
+	doneCmd.Flags().IntVarP(&donePriority, "priority", "p", -1, "Override priority (0-4, default: inherit from issue)")
+
+	rootCmd.AddCommand(doneCmd)
+}
+
+func runDone(cmd *cobra.Command, args []string) error {
+	// Find workspace
+	townRoot, err := workspace.FindFromCwdOrError()
+	if err != nil {
+		return fmt.Errorf("not in a Gas Town workspace: %w", err)
+	}
+
+	// Find current rig
+	rigName, _, err := findCurrentRig(townRoot)
+	if err != nil {
+		return err
+	}
+
+	// Initialize git for the current directory
+	cwd, err := os.Getwd()
+	if err != nil {
+		return fmt.Errorf("getting current directory: %w", err)
+	}
+	g := git.NewGit(cwd)
+
+	// Get current branch
+	branch, err := g.CurrentBranch()
+	if err != nil {
+		return fmt.Errorf("getting current branch: %w", err)
+	}
+
+	if branch == "main" || branch == "master" {
+		return fmt.Errorf("cannot submit main/master branch to merge queue")
+	}
+
+	// Parse branch info
+	info := parseBranchName(branch)
+
+	// Override with explicit flags
+	issueID := doneIssue
+	if issueID == "" {
+		issueID = info.Issue
+	}
+	worker := info.Worker
+
+	if issueID == "" {
+		return fmt.Errorf("cannot determine source issue from branch '%s'; use --issue to specify", branch)
+	}
+
+	// Initialize beads
+	bd := beads.New(cwd)
+
+	// Determine target branch (auto-detect integration branch if applicable)
+	target := "main"
+	autoTarget, err := detectIntegrationBranch(bd, g, issueID)
+	if err == nil && autoTarget != "" {
+		target = autoTarget
+	}
+
+	// Get source issue for priority inheritance
+	var priority int
+	if donePriority >= 0 {
+		priority = donePriority
+	} else {
+		// Try to inherit from source issue
+		sourceIssue, err := bd.Show(issueID)
+		if err != nil {
+			priority = 2 // Default
+		} else {
+			priority = sourceIssue.Priority
+		}
+	}
+
+	// Build title
+	title := fmt.Sprintf("Merge: %s", issueID)
+
+	// Build description with MR fields
+	mrFields := &beads.MRFields{
+		Branch:      branch,
+		Target:      target,
+		SourceIssue: issueID,
+		Worker:      worker,
+		Rig:         rigName,
+	}
+	description := beads.FormatMRFields(mrFields)
+
+	// Create the merge-request issue
+	createOpts := beads.CreateOptions{
+		Title:       title,
+		Type:        "merge-request",
+		Priority:    priority,
+		Description: description,
+	}
+
+	issue, err := bd.Create(createOpts)
+	if err != nil {
+		return fmt.Errorf("creating merge request: %w", err)
+	}
+
+	// Success output
+	fmt.Printf("%s Work submitted to merge queue\n", style.Bold.Render("✓"))
+	fmt.Printf("  MR ID: %s\n", style.Bold.Render(issue.ID))
+	fmt.Printf("  Source: %s\n", branch)
+	fmt.Printf("  Target: %s\n", target)
+	fmt.Printf("  Issue: %s\n", issueID)
+	if worker != "" {
+		fmt.Printf("  Worker: %s\n", worker)
+	}
+	fmt.Printf("  Priority: P%d\n", priority)
+	fmt.Println()
+	fmt.Printf("%s\n", style.Dim.Render("The Refinery will process your merge request."))
+
+	return nil
+}