fix(create): persist and display Demo and Module item ordering #182

Problem

Reordering exercises in the Demo editor must persist and display in the configured top-to-bottom order. Module resource selection must support adding several resources into a visible draggable list, preserving its top-to-bottom order across save and reload.

Scope and approach\

Demo exercises

• Retain the existing DemoExercises.order schema and update behavior; no new Demo ordering model or migration is needed.
• Ensure the learner-facing GET /api/demos/:uid/attempt query orders exercises by DemoExercises.order ASC.
• Verify the existing Demo editor drag state is submitted as the ordered exercise-ID array and is restored after saving and reopening.

Module resources

• Add an ordering column to ModuleResources, with a deterministic backfill.
• Introduce/register an explicit ModuleResources join model and use it for the Module-Resource association.
• On module creation and update, persist each resource association using the submitted resource-ID order.
• Apply resource ordering to every relevant read path: module create/update reloads, module GET/list, course/student-course payloads, and the module-resource SQL used by the Demo attempt endpoint.
• Replace the Module form’s multiselect presentation with a cleared single-select picker and visible selected-resource rows below it. Exclude already selected resources, allow removal, and reuse the existing @dnd-kit sortable interaction for top-to-bottom reordering.
• Correct the Module draft type so its resource state is ordered IDs (or equivalent selected-item data), removing the existing Resource[]/ID mismatch and @ts-ignore workarounds.

Acceptance criteria\

• Dragging and saving a Demo’s exercises preserves that order when reopening its editor and on the learner Read view
• A Module user can select multiple resources one at a time; each appears below the selector, can be removed, and can be reordered by drag-and-drop.
• Saving and reopening a Module retains the configured resource order.\n- [ ] Module resources are returned in that order from all affected API/read paths.
• Tests cover persisted/retrieved API ordering plus Demo and Module editor interactions.

Verification

• API tests for Demo attempt exercise order and Module resource order after update/reload.
• Component or Cypress coverage for Demo drag-save-reopen and Module multi-select, reorder, save, and reopen.
• Run the relevant test suites and production client/API builds.