feat(tmux): add per-rig color themes and dynamic status line (gt-vc1n)

Add tmux status bar theming for Gas Town sessions:

- Per-rig color themes auto-assigned via consistent hashing
- 10 curated dark themes (ocean, forest, rust, plum, etc.)
- Special gold/dark theme for Mayor
- Dynamic status line showing current issue and mail count
- Mayor status shows polecat/rig counts

New commands:
- gt theme --list: show available themes
- gt theme apply: apply to running sessions
- gt issue set/clear: agents update their current issue
- gt status-line: internal command for tmux refresh

Status bar format:
- Left: [rig/worker] role
- Right: <issue> | <mail> | HH:MM

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

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

internal/cmd/statusline.go

@@ -0,0 +1,145 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/mail"
+	"github.com/steveyegge/gastown/internal/tmux"
+)
+
+var (
+	statusLineSession string
+)
+
+var statusLineCmd = &cobra.Command{
+	Use:    "status-line",
+	Short:  "Output status line content for tmux (internal use)",
+	Hidden: true, // Internal command called by tmux
+	RunE:   runStatusLine,
+}
+
+func init() {
+	rootCmd.AddCommand(statusLineCmd)
+	statusLineCmd.Flags().StringVar(&statusLineSession, "session", "", "Tmux session name")
+}
+
+func runStatusLine(cmd *cobra.Command, args []string) error {
+	t := tmux.NewTmux()
+
+	// Get session environment
+	var rigName, polecat, crew, issue, role string
+
+	if statusLineSession != "" {
+		rigName, _ = t.GetEnvironment(statusLineSession, "GT_RIG")
+		polecat, _ = t.GetEnvironment(statusLineSession, "GT_POLECAT")
+		crew, _ = t.GetEnvironment(statusLineSession, "GT_CREW")
+		issue, _ = t.GetEnvironment(statusLineSession, "GT_ISSUE")
+		role, _ = t.GetEnvironment(statusLineSession, "GT_ROLE")
+	} else {
+		// Fallback to process environment
+		rigName = os.Getenv("GT_RIG")
+		polecat = os.Getenv("GT_POLECAT")
+		crew = os.Getenv("GT_CREW")
+		issue = os.Getenv("GT_ISSUE")
+		role = os.Getenv("GT_ROLE")
+	}
+
+	// Determine identity and output based on role
+	if role == "mayor" || statusLineSession == "gt-mayor" {
+		return runMayorStatusLine(t)
+	}
+
+	// Build mail identity
+	var identity string
+	if rigName != "" {
+		if polecat != "" {
+			identity = fmt.Sprintf("%s/%s", rigName, polecat)
+		} else if crew != "" {
+			identity = fmt.Sprintf("%s/%s", rigName, crew)
+		}
+	}
+
+	// Build status parts
+	var parts []string
+
+	// Current issue
+	if issue != "" {
+		parts = append(parts, issue)
+	}
+
+	// Mail count
+	if identity != "" {
+		unread := getUnreadMailCount(identity)
+		if unread > 0 {
+			parts = append(parts, fmt.Sprintf("\U0001F4EC %d", unread)) // mail emoji
+		}
+	}
+
+	// Output
+	if len(parts) > 0 {
+		fmt.Print(strings.Join(parts, " | ") + " |")
+	}
+
+	return nil
+}
+
+func runMayorStatusLine(t *tmux.Tmux) error {
+	// Count active sessions by listing tmux sessions
+	sessions, err := t.ListSessions()
+	if err != nil {
+		return nil // Silent fail
+	}
+
+	// Count gt-* sessions (polecats) and rigs
+	polecatCount := 0
+	rigs := make(map[string]bool)
+	for _, s := range sessions {
+		if strings.HasPrefix(s, "gt-") && s != "gt-mayor" {
+			polecatCount++
+			// Extract rig name: gt-<rig>-<worker>
+			parts := strings.SplitN(s, "-", 3)
+			if len(parts) >= 2 {
+				rigs[parts[1]] = true
+			}
+		}
+	}
+	rigCount := len(rigs)
+
+	// Get mayor mail
+	unread := getUnreadMailCount("mayor/")
+
+	// Build status
+	var parts []string
+	parts = append(parts, fmt.Sprintf("%d polecats", polecatCount))
+	parts = append(parts, fmt.Sprintf("%d rigs", rigCount))
+	if unread > 0 {
+		parts = append(parts, fmt.Sprintf("\U0001F4EC %d", unread))
+	}
+
+	fmt.Print(strings.Join(parts, " | ") + " |")
+	return nil
+}
+
+// getUnreadMailCount returns unread mail count for an identity.
+// Fast path - returns 0 on any error.
+func getUnreadMailCount(identity string) int {
+	// Find workspace
+	workDir, err := findBeadsWorkDir()
+	if err != nil {
+		return 0
+	}
+
+	// Create mailbox using beads
+	mailbox := mail.NewMailboxBeads(identity, workDir)
+
+	// Get count
+	_, unread, err := mailbox.Count()
+	if err != nil {
+		return 0
+	}
+
+	return unread
+}