feat: Add overseer identity for human operator mail support

Adds first-class support for the human overseer in Gas Town mail:

- New OverseerConfig in internal/config/overseer.go with identity
  detection (git config, gh cli, environment)
- Overseer detected/saved on town install (mayor/overseer.json)
- Simplified detectSender(): GT_ROLE set = agent, else = overseer
- New overseer address alongside mayor/ and deacon/
- Added --cc flag to mail send for CC recipients
- Inbox now includes CC'd messages via label query
- gt status shows overseer identity and unread mail count
- New gt whoami command shows current mail identity

Generated with Claude Code

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

internal/cmd/whoami.go

@@ -0,0 +1,80 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/config"
+	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+var whoamiCmd = &cobra.Command{
+	Use:     "whoami",
+	GroupID: GroupDiag,
+	Short:   "Show current identity for mail commands",
+	Long: `Show the identity that will be used for mail commands.
+
+Identity is determined by:
+1. GT_ROLE env var (if set) - indicates an agent session
+2. No GT_ROLE - you are the overseer (human)
+
+Use --identity flag with mail commands to override.
+
+Examples:
+  gt whoami                      # Show current identity
+  gt mail inbox                  # Check inbox for current identity
+  gt mail inbox --identity mayor/  # Check Mayor's inbox instead`,
+	RunE: runWhoami,
+}
+
+func init() {
+	rootCmd.AddCommand(whoamiCmd)
+}
+
+func runWhoami(cmd *cobra.Command, args []string) error {
+	// Get current identity using same logic as mail commands
+	identity := detectSender()
+
+	fmt.Printf("%s %s\n", style.Bold.Render("Identity:"), identity)
+
+	// Show how it was determined
+	gtRole := os.Getenv("GT_ROLE")
+	if gtRole != "" {
+		fmt.Printf("%s GT_ROLE=%s\n", style.Dim.Render("Source:"), gtRole)
+
+		// Show additional env vars if present
+		if rig := os.Getenv("GT_RIG"); rig != "" {
+			fmt.Printf("%s GT_RIG=%s\n", style.Dim.Render("       "), rig)
+		}
+		if polecat := os.Getenv("GT_POLECAT"); polecat != "" {
+			fmt.Printf("%s GT_POLECAT=%s\n", style.Dim.Render("       "), polecat)
+		}
+		if crew := os.Getenv("GT_CREW"); crew != "" {
+			fmt.Printf("%s GT_CREW=%s\n", style.Dim.Render("       "), crew)
+		}
+	} else {
+		fmt.Printf("%s no GT_ROLE set (human at terminal)\n", style.Dim.Render("Source:"))
+
+		// If overseer, show their configured identity
+		if identity == "overseer" {
+			townRoot, err := workspace.FindFromCwd()
+			if err == nil && townRoot != "" {
+				if overseerConfig, err := config.LoadOverseerConfig(config.OverseerConfigPath(townRoot)); err == nil {
+					fmt.Printf("\n%s\n", style.Bold.Render("Overseer Identity:"))
+					fmt.Printf("  Name:  %s\n", overseerConfig.Name)
+					if overseerConfig.Email != "" {
+						fmt.Printf("  Email: %s\n", overseerConfig.Email)
+					}
+					if overseerConfig.Username != "" {
+						fmt.Printf("  User:  %s\n", overseerConfig.Username)
+					}
+					fmt.Printf("  %s %s\n", style.Dim.Render("(detected via"), style.Dim.Render(overseerConfig.Source+")"))
+				}
+			}
+		}
+	}
+
+	return nil
+}