feat: add reverse mode to dependency tree traversal

- Add reverse parameter to GetDependencyTree interface
- Implement reverse SQL traversal (dependents vs dependencies)
- Add comprehensive test for reverse mode (TDD: test-first approach)
- Update existing test calls with reverse=false for backward compatibility

Reverse mode inverts tree direction to show dependents instead of dependencies:
- Normal: JOIN dependencies d ON i.id = d.depends_on_id (traverse UP)
- Reverse: JOIN dependencies d ON i.id = d.issue_id (traverse DOWN)

All storage tests passing. No regressions.

internal/storage/sqlite/dependencies_test.go

@@ -249,7 +249,7 @@ func TestGetDependencyTree(t *testing.T) {
 	store.AddDependency(ctx, &types.Dependency{IssueID: issue3.ID, DependsOnID: issue2.ID, Type: types.DepBlocks}, "test-user")
 
 	// Get tree starting from issue3
-	tree, err := store.GetDependencyTree(ctx, issue3.ID, 10, false)
+	tree, err := store.GetDependencyTree(ctx, issue3.ID, 10, false, false)
 	if err != nil {
 		t.Fatalf("GetDependencyTree failed: %v", err)
 	}
@@ -311,7 +311,7 @@ func TestGetDependencyTree_TruncationDepth(t *testing.T) {
 	}
 
 	// Get tree with maxDepth=2 (should only get 3 nodes: depths 0, 1, 2)
-	tree, err := store.GetDependencyTree(ctx, issues[4].ID, 2, false)
+	tree, err := store.GetDependencyTree(ctx, issues[4].ID, 2, false, false)
 	if err != nil {
 		t.Fatalf("GetDependencyTree failed: %v", err)
 	}
@@ -354,7 +354,7 @@ func TestGetDependencyTree_DefaultDepth(t *testing.T) {
 	}, "test-user")
 
 	// Get tree with default depth (50)
-	tree, err := store.GetDependencyTree(ctx, issue2.ID, 50, false)
+	tree, err := store.GetDependencyTree(ctx, issue2.ID, 50, false, false)
 	if err != nil {
 		t.Fatalf("GetDependencyTree failed: %v", err)
 	}
@@ -399,7 +399,7 @@ func TestGetDependencyTree_MaxDepthOne(t *testing.T) {
 	}, "test-user")
 
 	// Get tree with maxDepth=1 (should get root + one level)
-	tree, err := store.GetDependencyTree(ctx, issue3.ID, 1, false)
+	tree, err := store.GetDependencyTree(ctx, issue3.ID, 1, false, false)
 	if err != nil {
 		t.Fatalf("GetDependencyTree failed: %v", err)
 	}
@@ -725,3 +725,78 @@ func TestCrossTypeCyclePreventionThreeIssues(t *testing.T) {
 		t.Errorf("Expected no cycles after prevention, but found %d", len(cycles))
 	}
 }
+
+func TestGetDependencyTree_Reverse(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+	ctx := context.Background()
+
+	// Create a dependency chain: issue1 <- issue2 <- issue3
+	// (issue3 depends on issue2, issue2 depends on issue1)
+	issue1 := &types.Issue{
+		Title:     "Base issue",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+	issue2 := &types.Issue{
+		Title:     "Depends on issue1",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+	issue3 := &types.Issue{
+		Title:     "Depends on issue2",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+
+	store.CreateIssue(ctx, issue1, "test")
+	store.CreateIssue(ctx, issue2, "test")
+	store.CreateIssue(ctx, issue3, "test")
+
+	// Create dependencies: issue3 → issue2 → issue1
+	dep1 := &types.Dependency{IssueID: issue2.ID, DependsOnID: issue1.ID, Type: types.DepBlocks}
+	dep2 := &types.Dependency{IssueID: issue3.ID, DependsOnID: issue2.ID, Type: types.DepBlocks}
+	store.AddDependency(ctx, dep1, "test")
+	store.AddDependency(ctx, dep2, "test")
+
+	// Test normal mode: from issue3, should traverse UP to issue1
+	normalTree, err := store.GetDependencyTree(ctx, issue3.ID, 10, false, false)
+	if err != nil {
+		t.Fatalf("GetDependencyTree normal mode failed: %v", err)
+	}
+	if len(normalTree) != 3 {
+		t.Fatalf("Expected 3 nodes in normal tree, got %d", len(normalTree))
+	}
+
+	// Test reverse mode: from issue1, should traverse DOWN to issue3
+	reverseTree, err := store.GetDependencyTree(ctx, issue1.ID, 10, false, true)
+	if err != nil {
+		t.Fatalf("GetDependencyTree reverse mode failed: %v", err)
+	}
+	if len(reverseTree) != 3 {
+		t.Fatalf("Expected 3 nodes in reverse tree, got %d", len(reverseTree))
+	}
+
+	// Verify reverse tree structure: issue1 at depth 0
+	depthMap := make(map[string]int)
+	for _, node := range reverseTree {
+		depthMap[node.ID] = node.Depth
+	}
+
+	if depthMap[issue1.ID] != 0 {
+		t.Errorf("Expected depth 0 for %s in reverse tree, got %d", issue1.ID, depthMap[issue1.ID])
+	}
+
+	// issue2 should be at depth 1 (depends on issue1)
+	if depthMap[issue2.ID] != 1 {
+		t.Errorf("Expected depth 1 for %s in reverse tree, got %d", issue2.ID, depthMap[issue2.ID])
+	}
+
+	// issue3 should be at depth 2 (depends on issue2)
+	if depthMap[issue3.ID] != 2 {
+		t.Errorf("Expected depth 2 for %s in reverse tree, got %d", issue3.ID, depthMap[issue3.ID])
+	}
+}