fix(mail): add crew worker detection in detectSender()

detectSender() only detected polecats, not crew workers. Crew workers
like Emma at /Users/stevey/gt/beads/crew/emma were incorrectly
defaulting to mayor/ instead of getting their proper address.

Added /crew/ directory pattern matching parallel to the existing
/polecats/ detection, extracting rig/crewName address format.

Fixes: gt-70b3

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

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

internal/cmd/mail.go

@@ -468,6 +468,17 @@ func detectSender() string {
 		}
 	}
 
+	// If in a rig's crew directory, extract address
+	if strings.Contains(cwd, "/crew/") {
+		parts := strings.Split(cwd, "/crew/")
+		if len(parts) >= 2 {
+			rigPath := parts[0]
+			crewName := strings.Split(parts[1], "/")[0]
+			rigName := filepath.Base(rigPath)
+			return fmt.Sprintf("%s/%s", rigName, crewName)
+		}
+	}
+
 	// Default to mayor
 	return "mayor/"
 }