feat(ready): add --type flag for filtering by issue type (gt-ktf3)

Enables bd ready --type=merge-request for MQ integration.
The Engineer can now query for ready merge-requests.

Files changed:
- cmd/bd/ready.go: Add -t/--type flag
- internal/types/types.go: Add Type field to WorkFilter
- internal/rpc/protocol.go: Add Type to ReadyArgs
- internal/storage/sqlite/ready.go: Filter by issue_type column

internal/rpc/protocol.go

@@ -214,6 +214,7 @@ type ReadyArgs struct {
 	Assignee   string   `json:"assignee,omitempty"`
 	Unassigned bool     `json:"unassigned,omitempty"`
 	Priority   *int     `json:"priority,omitempty"`
+	Type       string   `json:"type,omitempty"`
 	Limit      int      `json:"limit,omitempty"`
 	SortPolicy string   `json:"sort_policy,omitempty"`
 	Labels     []string `json:"labels,omitempty"`