perf(list): optimize bd list --json to fetch only needed dependencies (#1316)

Add GetDependencyRecordsForIssues method to storage interface that
fetches dependencies only for specified issue IDs instead of all
dependencies in the database.

This optimizes bd list --json which previously called
GetAllDependencyRecords() even when displaying only a few issues
(e.g., bd list --limit 10).

- Add GetDependencyRecordsForIssues to Storage interface
- Implement in SQLite, Dolt, and Memory backends
- Update list.go JSON output to use targeted method
- Update mock storage in tests

Origin: Mayor's review of PR #1296

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

internal/storage/storage_test.go

@@ -69,6 +69,9 @@ func (m *mockStorage) GetDependencyRecords(ctx context.Context, issueID string)
 func (m *mockStorage) GetAllDependencyRecords(ctx context.Context) (map[string][]*types.Dependency, error) {
 	return nil, nil
 }
+func (m *mockStorage) GetDependencyRecordsForIssues(ctx context.Context, issueIDs []string) (map[string][]*types.Dependency, error) {
+	return nil, nil
+}
 func (m *mockStorage) GetDependencyCounts(ctx context.Context, issueIDs []string) (map[string]*types.DependencyCounts, error) {
 	return nil, nil
 }