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/mail/types.go

@@ -4,6 +4,7 @@ package mail
 import (
 	"crypto/rand"
 	"encoding/hex"
+	"strings"
 	"time"
 )
 
@@ -142,23 +143,45 @@ func generateThreadID() string {
 	return "thread-" + hex.EncodeToString(b)
 }
 
-// BeadsMessage represents a message as returned by bd mail commands.
+// BeadsMessage represents a message as returned by bd list/show commands.
+// Messages are beads issues with type=message and metadata stored in labels.
 type BeadsMessage struct {
 	ID          string    `json:"id"`
 	Title       string    `json:"title"`       // Subject
 	Description string    `json:"description"` // Body
-	Sender      string    `json:"sender"`      // From identity
 	Assignee    string    `json:"assignee"`    // To identity
 	Priority    int       `json:"priority"`    // 0=urgent, 1=high, 2=normal, 3=low
 	Status      string    `json:"status"`      // open=unread, closed=read
 	CreatedAt   time.Time `json:"created_at"`
-	Type        string    `json:"type,omitempty"`      // Message type
-	ThreadID    string    `json:"thread_id,omitempty"` // Thread identifier
-	ReplyTo     string    `json:"reply_to,omitempty"`  // Original message ID
+	Labels      []string  `json:"labels"` // Metadata labels (from:X, thread:X, reply-to:X, msg-type:X)
+
+	// Cached parsed values (populated by ParseLabels)
+	sender   string
+	threadID string
+	replyTo  string
+	msgType  string
+}
+
+// ParseLabels extracts metadata from the labels array.
+func (bm *BeadsMessage) ParseLabels() {
+	for _, label := range bm.Labels {
+		if strings.HasPrefix(label, "from:") {
+			bm.sender = strings.TrimPrefix(label, "from:")
+		} else if strings.HasPrefix(label, "thread:") {
+			bm.threadID = strings.TrimPrefix(label, "thread:")
+		} else if strings.HasPrefix(label, "reply-to:") {
+			bm.replyTo = strings.TrimPrefix(label, "reply-to:")
+		} else if strings.HasPrefix(label, "msg-type:") {
+			bm.msgType = strings.TrimPrefix(label, "msg-type:")
+		}
+	}
 }
 
 // ToMessage converts a BeadsMessage to a GGT Message.
 func (bm *BeadsMessage) ToMessage() *Message {
+	// Parse labels to extract metadata
+	bm.ParseLabels()
+
 	// Convert beads priority (0=urgent, 1=high, 2=normal, 3=low) to GGT Priority
 	var priority Priority
 	switch bm.Priority {
@@ -174,14 +197,14 @@ func (bm *BeadsMessage) ToMessage() *Message {
 
 	// Convert message type, default to notification
 	msgType := TypeNotification
-	switch MessageType(bm.Type) {
+	switch MessageType(bm.msgType) {
 	case TypeTask, TypeScavenge, TypeReply:
-		msgType = MessageType(bm.Type)
+		msgType = MessageType(bm.msgType)
 	}
 
 	return &Message{
 		ID:        bm.ID,
-		From:      identityToAddress(bm.Sender),
+		From:      identityToAddress(bm.sender),
 		To:        identityToAddress(bm.Assignee),
 		Subject:   bm.Title,
 		Body:      bm.Description,
@@ -189,8 +212,8 @@ func (bm *BeadsMessage) ToMessage() *Message {
 		Read:      bm.Status == "closed",
 		Priority:  priority,
 		Type:      msgType,
-		ThreadID:  bm.ThreadID,
-		ReplyTo:   bm.ReplyTo,
+		ThreadID:  bm.threadID,
+		ReplyTo:   bm.replyTo,
 	}
 }