refactor(mail): Remove bd mail dependency, use bd create/list/show (gt-9xg)

Replace `bd mail send/inbox/read/ack` commands with `bd create/list/show/close`.
This separates the orchestration layer (gt) from the data plane (beads).

Changes:
- router.go: Use `bd create --type=message` instead of `bd mail send`
- mailbox.go: Use `bd list --type=message` and `bd show` for inbox/read
- types.go: Parse metadata from labels (from:, thread:, reply-to:)
- mail.go: Fix findBeadsWorkDir to prefer rig-level beads, fix crew address format

Messages are now stored as beads issues with type=message. Metadata (sender,
thread, reply-to) is stored in labels for retrieval.

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

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

internal/cmd/mail.go

@@ -462,16 +462,8 @@ func runMailDelete(cmd *cobra.Command, args []string) error {
 // findBeadsWorkDir finds a directory with a .beads database.
 // Walks up from CWD looking for .beads/ directory.
 func findBeadsWorkDir() (string, error) {
-	// First try workspace root
-	townRoot, err := workspace.FindFromCwdOrError()
-	if err == nil {
-		// Check if town root has .beads
-		if _, err := os.Stat(filepath.Join(townRoot, ".beads")); err == nil {
-			return townRoot, nil
-		}
-	}
-
-	// Walk up from CWD looking for .beads
+	// Walk up from CWD looking for .beads - prefer closest one (rig-level)
+	// This finds the rig's .beads before the town's .beads
 	cwd, err := os.Getwd()
 	if err != nil {
 		return "", err
@@ -490,6 +482,14 @@ func findBeadsWorkDir() (string, error) {
 		path = parent
 	}
 
+	// Fall back to town root if nothing found walking up
+	townRoot, err := workspace.FindFromCwdOrError()
+	if err == nil {
+		if _, err := os.Stat(filepath.Join(townRoot, ".beads")); err == nil {
+			return townRoot, nil
+		}
+	}
+
 	return "", fmt.Errorf("no .beads directory found")
 }
 
@@ -520,14 +520,14 @@ func detectSender() string {
 		}
 	}
 
-	// If in a rig's crew directory, extract address
+	// If in a rig's crew directory, extract address (format: rig/crew/name)
 	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)
+			return fmt.Sprintf("%s/crew/%s", rigName, crewName)
 		}
 	}