fix(doctor): Preserve parent-child dependencies in child→parent check (GH#750)

The CheckChildParentDependencies detection and ChildParentDependencies fix
were flagging ALL child→parent dependencies, including legitimate
'parent-child' type structural hierarchy relationships.

Now only blocking types (blocks, conditional-blocks, waits-for) are
detected as anti-patterns. The 'parent-child' type is a legitimate
hierarchy marker used for:
- Tracking parent-child relationships
- Transitive block propagation (if parent blocked, children blocked)
- Hierarchy visualization in external tools

Changes:
- Add type filter to SELECT queries (only blocking types)
- Add type filter to DELETE statement (preserve parent-child)
- Add regression test TestChildParentDependencies_PreservesParentChildType

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor/fix/validation.go

@@ -180,11 +180,14 @@ func ChildParentDependencies(path string) error {
 	}
 	defer db.Close()
 
-	// Find child→parent dependencies where issue_id starts with depends_on_id + "."
+	// Find child→parent BLOCKING dependencies where issue_id starts with depends_on_id + "."
+	// Only matches blocking types (blocks, conditional-blocks, waits-for) that cause deadlock.
+	// Excludes 'parent-child' type which is a legitimate structural hierarchy relationship.
 	query := `
-		SELECT d.issue_id, d.depends_on_id
+		SELECT d.issue_id, d.depends_on_id, d.type
 		FROM dependencies d
 		WHERE d.issue_id LIKE d.depends_on_id || '.%'
+		  AND d.type IN ('blocks', 'conditional-blocks', 'waits-for')
 	`
 	rows, err := db.Query(query)
 	if err != nil {
@@ -195,12 +198,13 @@ func ChildParentDependencies(path string) error {
 	type badDep struct {
 		issueID     string
 		dependsOnID string
+		depType     string
 	}
 	var badDeps []badDep
 
 	for rows.Next() {
 		var d badDep
-		if err := rows.Scan(&d.issueID, &d.dependsOnID); err == nil {
+		if err := rows.Scan(&d.issueID, &d.dependsOnID, &d.depType); err == nil {
 			badDeps = append(badDeps, d)
 		}
 	}
@@ -210,10 +214,10 @@ func ChildParentDependencies(path string) error {
 		return nil
 	}
 
-	// Delete child→parent dependencies
+	// Delete child→parent blocking dependencies (preserving parent-child type)
 	for _, d := range badDeps {
-		_, err := db.Exec("DELETE FROM dependencies WHERE issue_id = ? AND depends_on_id = ?",
-			d.issueID, d.dependsOnID)
+		_, err := db.Exec("DELETE FROM dependencies WHERE issue_id = ? AND depends_on_id = ? AND type = ?",
+			d.issueID, d.dependsOnID, d.depType)
 		if err != nil {
 			fmt.Printf("  Warning: failed to remove %s→%s: %v\n", d.issueID, d.dependsOnID, err)
 		} else {