Add YouTrack pull/push sync with project settings and time tracking.

Wire manual Y menu and CLI sync for issues and work items, persist
per-project credentials, and keep local edits until an explicit push.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/ticket/ticket.go

@@ -50,6 +50,11 @@ func (s Status) Index() int {
 	return 0
 }
 
+const (
+	// SourceYouTrack marks tickets imported from YouTrack.
+	SourceYouTrack = "youtrack"
+)
+
 // Ticket is the domain model for a work item.
 // Title (headline) and Description are Markdown.
 type Ticket struct {
@@ -60,4 +65,10 @@ type Ticket struct {
 	ProjectID   string    `json:"projectId"`
 	CreatedAt   time.Time `json:"createdAt"`
 	UpdatedAt   time.Time `json:"updatedAt"`
+
+	// External sync (optional). Local UUID stays in ID.
+	Source      string    `json:"source,omitempty"`
+	ExternalID  string    `json:"externalId,omitempty"`
+	ExternalURL string    `json:"externalUrl,omitempty"`
+	SyncedAt    time.Time `json:"syncedAt,omitempty"`
 }