Fix code review issues bd-19 through bd-23

- bd-19: Fix import zero-value field handling using JSON presence detection
- bd-20: Add --strict flag for dependency import failures
- bd-21: Simplify getNextID SQL query (reduce params from 4 to 2)
- bd-22: Add validation/warning for malformed issue IDs
- bd-23: Optimize export dependency queries (fix N+1 problem)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/storage/storage.go

@@ -22,6 +22,7 @@ type Storage interface {
 	GetDependencies(ctx context.Context, issueID string) ([]*types.Issue, error)
 	GetDependents(ctx context.Context, issueID string) ([]*types.Issue, error)
 	GetDependencyRecords(ctx context.Context, issueID string) ([]*types.Dependency, error)
+	GetAllDependencyRecords(ctx context.Context) (map[string][]*types.Dependency, error)
 	GetDependencyTree(ctx context.Context, issueID string, maxDepth int) ([]*types.TreeNode, error)
 	DetectCycles(ctx context.Context) ([][]*types.Issue, error)