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/memory/memory.go

@@ -875,6 +875,20 @@ func (m *MemoryStorage) GetAllDependencyRecords(ctx context.Context) (map[string
 	return result, nil
 }
 
+// GetDependencyRecordsForIssues returns dependency records for specific issues
+func (m *MemoryStorage) GetDependencyRecordsForIssues(ctx context.Context, issueIDs []string) (map[string][]*types.Dependency, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	result := make(map[string][]*types.Dependency)
+	for _, id := range issueIDs {
+		if deps, ok := m.dependencies[id]; ok {
+			result[id] = deps
+		}
+	}
+	return result, nil
+}
+
 // GetDirtyIssueHash returns the hash for dirty issue tracking
 func (m *MemoryStorage) GetDirtyIssueHash(ctx context.Context, issueID string) (string, error) {
 	// Memory storage doesn't track dirty hashes, return empty string