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.go

@@ -101,6 +101,7 @@ type Storage interface {
 	GetDependentsWithMetadata(ctx context.Context, issueID string) ([]*types.IssueWithDependencyMetadata, error)
 	GetDependencyRecords(ctx context.Context, issueID string) ([]*types.Dependency, error)
 	GetAllDependencyRecords(ctx context.Context) (map[string][]*types.Dependency, error)
+	GetDependencyRecordsForIssues(ctx context.Context, issueIDs []string) (map[string][]*types.Dependency, error)
 	GetDependencyCounts(ctx context.Context, issueIDs []string) (map[string]*types.DependencyCounts, error)
 	GetDependencyTree(ctx context.Context, issueID string, maxDepth int, showAllPaths bool, reverse bool) ([]*types.TreeNode, error)
 	DetectCycles(ctx context.Context) ([][]*types.Issue, error)