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/types/types.go

@@ -478,6 +478,7 @@ func (s SortPolicy) IsValid() bool {
 // WorkFilter is used to filter ready work queries
 type WorkFilter struct {
 	Status     Status
+	Type       string     // Filter by issue type (task, bug, feature, epic, merge-request, etc.)
 	Priority   *int
 	Assignee   *string
 	Unassigned bool       // Filter for issues with no assignee