Add --show-all-paths flag to bd dep tree

Implements bd-9: Allow users to view all paths through diamond dependencies
without deduplication. Useful for debugging complex dependency structures.

Changes:
- Added --show-all-paths flag to bd dep tree command
- Updated GetDependencyTree interface to accept showAllPaths parameter
- Modified deduplication logic to be conditional on flag
- Updated tests to pass new parameter

Amp-Thread-ID: https://ampcode.com/threads/T-43807dd5-8732-49ad-a839-cdb5dae70c35
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/storage.go

@@ -24,7 +24,7 @@ type Storage interface {
 	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)
+	GetDependencyTree(ctx context.Context, issueID string, maxDepth int, showAllPaths bool) ([]*types.TreeNode, error)
 	DetectCycles(ctx context.Context) ([][]*types.Issue, error)
 
 	// Labels