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/issue.go

@@ -0,0 +1,128 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/tmux"
+)
+
+var issueCmd = &cobra.Command{
+	Use:   "issue",
+	Short: "Manage current issue for status line display",
+}
+
+var issueSetCmd = &cobra.Command{
+	Use:   "set <issue-id>",
+	Short: "Set the current issue (shown in tmux status line)",
+	Args:  cobra.ExactArgs(1),
+	RunE:  runIssueSet,
+}
+
+var issueClearCmd = &cobra.Command{
+	Use:   "clear",
+	Short: "Clear the current issue from status line",
+	RunE:  runIssueClear,
+}
+
+var issueShowCmd = &cobra.Command{
+	Use:   "show",
+	Short: "Show the current issue",
+	RunE:  runIssueShow,
+}
+
+func init() {
+	rootCmd.AddCommand(issueCmd)
+	issueCmd.AddCommand(issueSetCmd)
+	issueCmd.AddCommand(issueClearCmd)
+	issueCmd.AddCommand(issueShowCmd)
+}
+
+func runIssueSet(cmd *cobra.Command, args []string) error {
+	issueID := args[0]
+
+	// Get current tmux session
+	session := os.Getenv("TMUX_PANE")
+	if session == "" {
+		// Try to detect from GT env vars
+		session = detectCurrentSession()
+		if session == "" {
+			return fmt.Errorf("not in a tmux session")
+		}
+	}
+
+	t := tmux.NewTmux()
+	if err := t.SetEnvironment(session, "GT_ISSUE", issueID); err != nil {
+		return fmt.Errorf("setting issue: %w", err)
+	}
+
+	fmt.Printf("Issue set to: %s\n", issueID)
+	return nil
+}
+
+func runIssueClear(cmd *cobra.Command, args []string) error {
+	session := os.Getenv("TMUX_PANE")
+	if session == "" {
+		session = detectCurrentSession()
+		if session == "" {
+			return fmt.Errorf("not in a tmux session")
+		}
+	}
+
+	t := tmux.NewTmux()
+	// Set to empty string to clear
+	if err := t.SetEnvironment(session, "GT_ISSUE", ""); err != nil {
+		return fmt.Errorf("clearing issue: %w", err)
+	}
+
+	fmt.Println("Issue cleared")
+	return nil
+}
+
+func runIssueShow(cmd *cobra.Command, args []string) error {
+	session := os.Getenv("TMUX_PANE")
+	if session == "" {
+		session = detectCurrentSession()
+		if session == "" {
+			return fmt.Errorf("not in a tmux session")
+		}
+	}
+
+	t := tmux.NewTmux()
+	issue, err := t.GetEnvironment(session, "GT_ISSUE")
+	if err != nil {
+		return fmt.Errorf("getting issue: %w", err)
+	}
+
+	if issue == "" {
+		fmt.Println("No issue set")
+	} else {
+		fmt.Printf("Current issue: %s\n", issue)
+	}
+	return nil
+}
+
+// detectCurrentSession tries to find the tmux session name from env.
+func detectCurrentSession() string {
+	// Try to build session name from GT env vars
+	rig := os.Getenv("GT_RIG")
+	polecat := os.Getenv("GT_POLECAT")
+	crew := os.Getenv("GT_CREW")
+
+	if rig != "" {
+		if polecat != "" {
+			return fmt.Sprintf("gt-%s-%s", rig, polecat)
+		}
+		if crew != "" {
+			return fmt.Sprintf("gt-%s-crew-%s", rig, crew)
+		}
+	}
+
+	// Check if we're mayor
+	if os.Getenv("GT_ROLE") == "mayor" {
+		return "gt-mayor"
+	}
+
+	return ""
+}