Add role-based theming with layered config and doctor check

Role themes:
- witness: rust (red/alert)
- refinery: plum (purple)
- crew/polecat: inherit rig theme

Resolution order:
1. Per-rig role override (rig/.gastown/config.json role_themes)
2. Global role default (mayor/town.json theme.role_defaults)
3. Built-in role defaults
4. Rig theme (config or hash-based)

Config schema:
- TownConfig.Theme.RoleDefaults: global role->theme map
- RigConfig.Theme.RoleThemes: per-rig role overrides

Doctor check:
- Detects sessions with outdated theme format (brackets)
- Fixable with 'gt theme apply --all'

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

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

internal/doctor/theme_check.go

@@ -0,0 +1,116 @@
+package doctor
+
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"github.com/steveyegge/gastown/internal/tmux"
+)
+
+// ThemeCheck verifies tmux sessions have correct themes applied.
+type ThemeCheck struct {
+	FixableCheck
+}
+
+// NewThemeCheck creates a new theme check.
+func NewThemeCheck() *ThemeCheck {
+	return &ThemeCheck{
+		FixableCheck: FixableCheck{
+			BaseCheck: BaseCheck{
+				CheckName:        "themes",
+				CheckDescription: "Check tmux session theme configuration",
+			},
+		},
+	}
+}
+
+// Run checks if tmux sessions have themes applied correctly.
+func (c *ThemeCheck) Run(ctx *CheckContext) *CheckResult {
+	t := tmux.NewTmux()
+
+	// List all sessions
+	sessions, err := t.ListSessions()
+	if err != nil {
+		// No tmux server or error - not a problem, just skip
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusOK,
+			Message: "No tmux sessions running",
+		}
+	}
+
+	// Check for Gas Town sessions
+	var gtSessions []string
+	for _, s := range sessions {
+		if strings.HasPrefix(s, "gt-") {
+			gtSessions = append(gtSessions, s)
+		}
+	}
+
+	if len(gtSessions) == 0 {
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusOK,
+			Message: "No Gas Town sessions running",
+		}
+	}
+
+	// Check if sessions have proper status-left format (no brackets = new format)
+	var needsUpdate []string
+	for _, session := range gtSessions {
+		statusLeft, err := getSessionStatusLeft(session)
+		if err != nil {
+			continue
+		}
+		// Old format had brackets like [Mayor] or [gastown/crew]
+		if strings.Contains(statusLeft, "[") && strings.Contains(statusLeft, "]") {
+			needsUpdate = append(needsUpdate, session)
+		}
+	}
+
+	if len(needsUpdate) > 0 {
+		details := make([]string, len(needsUpdate))
+		for i, s := range needsUpdate {
+			details[i] = fmt.Sprintf("Needs update: %s", s)
+		}
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusWarning,
+			Message: fmt.Sprintf("%d session(s) have outdated theme format", len(needsUpdate)),
+			Details: details,
+			FixHint: "Run 'gt theme apply --all' or 'gt doctor --fix'",
+		}
+	}
+
+	return &CheckResult{
+		Name:    c.Name(),
+		Status:  StatusOK,
+		Message: fmt.Sprintf("%d session(s) have correct themes", len(gtSessions)),
+	}
+}
+
+// Fix applies themes to all sessions.
+func (c *ThemeCheck) Fix(ctx *CheckContext) error {
+	cmd := exec.Command("gt", "theme", "apply", "--all")
+	cmd.Dir = ctx.TownRoot
+	return cmd.Run()
+}
+
+// getSessionStatusLeft retrieves the status-left setting for a tmux session.
+func getSessionStatusLeft(session string) (string, error) {
+	cmd := exec.Command("tmux", "show-options", "-t", session, "status-left")
+	output, err := cmd.Output()
+	if err != nil {
+		return "", err
+	}
+	// Parse: status-left "value"
+	line := strings.TrimSpace(string(output))
+	if idx := strings.Index(line, "\""); idx != -1 {
+		end := strings.LastIndex(line, "\"")
+		if end > idx {
+			return line[idx+1 : end], nil
+		}
+	}
+	return line, nil
+}