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/storage/sqlite/sqlite.go

@@ -1673,6 +1673,16 @@ func (s *SQLiteStorage) SearchIssues(ctx context.Context, query string, filter t
 		}
 	}
 
+	// Label filtering (OR): issue must have AT LEAST ONE of these labels
+	if len(filter.LabelsAny) > 0 {
+		placeholders := make([]string, len(filter.LabelsAny))
+		for i, label := range filter.LabelsAny {
+			placeholders[i] = "?"
+			args = append(args, label)
+		}
+		whereClauses = append(whereClauses, fmt.Sprintf("id IN (SELECT issue_id FROM labels WHERE label IN (%s))", strings.Join(placeholders, ", ")))
+	}
+
 	whereSQL := ""
 	if len(whereClauses) > 0 {
 		whereSQL = "WHERE " + strings.Join(whereClauses, " AND ")