Add label and title filtering to bd list (closes #45, bd-269)

- Add --label/-l flag to filter issues by labels (AND logic)
- Add --title flag to filter issues by title substring
- Add TitleSearch field to IssueFilter type
- Implement label and title filtering in SearchIssues
- Perfect for worktree-specific issue management

Examples:
  bd list --label worktree,feature-x
  bd list --title "authentication"
  bd list --label worktree --title "bug"

internal/types/types.go

@@ -189,12 +189,13 @@ type Statistics struct {
 
 // IssueFilter is used to filter issue queries
 type IssueFilter struct {
-	Status    *Status
-	Priority  *int
-	IssueType *IssueType
-	Assignee  *string
-	Labels    []string
-	Limit     int
+	Status      *Status
+	Priority    *int
+	IssueType   *IssueType
+	Assignee    *string
+	Labels      []string
+	TitleSearch string
+	Limit       int
 }
 
 // WorkFilter is used to filter ready work queries