Add label filtering to bd list with AND/OR semantics

- Add --label flag for AND filtering (must have ALL labels)
- Add --label-any flag for OR filtering (must have AT LEAST ONE label)
- Add normalizeLabels() helper to trim, dedupe, and clean inputs
- Fix RPC title filtering parity bug (forward via Query field)
- Add comprehensive tests for label filtering including combined AND+OR
- Update documentation in README and CHANGELOG
- Improve flag help text to clarify combined semantics

Closes bd-161

internal/types/types.go

@@ -209,7 +209,8 @@ type IssueFilter struct {
 	Priority    *int
 	IssueType   *IssueType
 	Assignee    *string
-	Labels      []string
+	Labels      []string  // AND semantics: issue must have ALL these labels
+	LabelsAny   []string  // OR semantics: issue must have AT LEAST ONE of these labels
 	TitleSearch string
 	Limit       int
 }