Build Hierarchy Node Editor form UI

Use a BLoC (HierarchyNodeEditorBloc) with states: HierarchyNodeEditorInitial, HierarchyNodeEditorLoading, HierarchyNodeEditorValidationError (carries Map fieldErrors), HierarchyNodeEditorReady. The parent dropdown should use a StreamController with debounceTime(Duration(milliseconds: 300)) feeding into a Supabase .select().ilike('name', '%query%').limit(20).range() query. For cycle detection inline feedback, call the Hierarchy Structure Validator's pure-Dart method synchronously against the in-memory loaded tree (avoid a round-trip for this check). Depth-limit validation is a pure function: given the selected parent's depth, the proposed level's expected depth must equal parent_depth + 1.

Use Flutter's FocusTraversalGroup to enforce logical focus order. Wrap all error Text widgets in Semantics(liveRegion: true, child: ...) for proper screen-reader announcement. In edit mode, initialize BLoC with a HierarchyNodeEditorEditRequested(nodeId) event that pre-loads the node and populates form fields. Avoid StatefulWidget local state beyond TextEditingControllers — push all validation state into BLoC.

Unit tests (flutter_test): test LevelTypeSelector emits correct BLoC events on selection; test ParentUnitSearchDropdown debounce logic with fake timers (FakeAsync); test InlineValidationMessage renders correct text for each validation error type. Widget tests: pump HierarchyNodeEditorForm in both create and edit modes and verify field pre-population; verify submit button disabled state during async validation; verify focus traversal order using FocusNode.nextFocus() assertions. Accessibility tests: use flutter_test's SemanticsController to assert all fields have labels, error messages have liveRegion, and contrast ratios pass. Integration tests (on device/emulator): verify parent dropdown lazy-load triggers on scroll, search filters results, and debounce suppresses calls.

Target 85%+ line coverage on form widget and child components.