refactor: remove unused bd pin/unpin/hook commands (bd-x0zl)

Analysis found these commands are dead code:
- gt never calls `bd pin` - uses `bd update --status=pinned` instead
- Beads.Pin() wrapper exists but is never called
- bd hook functionality duplicated by gt mol status
- Code comment says "pinned field is cosmetic for bd hook visibility"

Removed:
- cmd/bd/pin.go
- cmd/bd/unpin.go
- cmd/bd/hook.go

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

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

cmd/bd/doctor/fix/validation_test.go

@@ -138,3 +138,66 @@ func TestChildParentDependencies_FixesBadDeps(t *testing.T) {
 		t.Errorf("Expected 2 dirty issues (unique issue_ids from removed deps), got %d", dirtyCount)
 	}
 }
+
+// TestChildParentDependencies_PreservesParentChildType verifies that legitimate
+// parent-child type dependencies are NOT removed (only blocking types are removed).
+// Regression test for GitHub issue #750.
+func TestChildParentDependencies_PreservesParentChildType(t *testing.T) {
+	// Set up test database with both 'blocks' and 'parent-child' type deps
+	dir := t.TempDir()
+	beadsDir := filepath.Join(dir, ".beads")
+	if err := os.MkdirAll(beadsDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	dbPath := filepath.Join(beadsDir, "beads.db")
+	db, err := openDB(dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Create schema with both 'blocks' (anti-pattern) and 'parent-child' (legitimate) deps
+	_, err = db.Exec(`
+		CREATE TABLE issues (id TEXT PRIMARY KEY);
+		CREATE TABLE dependencies (issue_id TEXT, depends_on_id TEXT, type TEXT);
+		CREATE TABLE dirty_issues (issue_id TEXT PRIMARY KEY);
+		INSERT INTO issues (id) VALUES ('bd-abc'), ('bd-abc.1'), ('bd-abc.2');
+		INSERT INTO dependencies (issue_id, depends_on_id, type) VALUES
+			('bd-abc.1', 'bd-abc', 'parent-child'),
+			('bd-abc.2', 'bd-abc', 'parent-child'),
+			('bd-abc.1', 'bd-abc', 'blocks');
+	`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	db.Close()
+
+	// Run fix
+	err = ChildParentDependencies(dir)
+	if err != nil {
+		t.Fatalf("ChildParentDependencies failed: %v", err)
+	}
+
+	// Verify only 'blocks' type was removed, 'parent-child' preserved
+	db, _ = openDB(dbPath)
+	defer db.Close()
+
+	var blocksCount int
+	db.QueryRow("SELECT COUNT(*) FROM dependencies WHERE type = 'blocks'").Scan(&blocksCount)
+	if blocksCount != 0 {
+		t.Errorf("Expected 0 'blocks' dependencies after fix, got %d", blocksCount)
+	}
+
+	var parentChildCount int
+	db.QueryRow("SELECT COUNT(*) FROM dependencies WHERE type = 'parent-child'").Scan(&parentChildCount)
+	if parentChildCount != 2 {
+		t.Errorf("Expected 2 'parent-child' dependencies preserved, got %d", parentChildCount)
+	}
+
+	// Verify only 1 dirty issue (the one with 'blocks' dep removed)
+	var dirtyCount int
+	db.QueryRow("SELECT COUNT(*) FROM dirty_issues").Scan(&dirtyCount)
+	if dirtyCount != 1 {
+		t.Errorf("Expected 1 dirty issue, got %d", dirtyCount)
+	}
+}