read the task category order from the items store

CATEGORY_ORDER hardcoded Video/Audio/Cleanup in the frontend, so adding a
category meant a code change. The order now lives in categories.yaml at the root
of the items store and reaches the client via GET /tasks/categories — the
platform no longer knows any category by name.

The endpoint is declared before /:name, which would otherwise match
"categories". Categories used by a task but absent from the file still work: they
sort alphabetically after the listed ones, and Other stays last.

Menus consume grouped tasks rather than grouping them per row. Groups are built
from the tasks and the file only ranks them, so a category listed with no
matching tasks cannot produce an empty submenu — locked in by tests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/api/tasks/tasks.ts

@@ -1,5 +1,5 @@
 import { createRouter } from '../../create-router';
-import { listTasks, getTaskByDirName, createTask, deleteTask } from './task-files';
+import { listTasks, getTaskByDirName, createTask, deleteTask, readCategoryOrder } from './task-files';
 
 type TriggerConfig = { type: 'file'; extensions: string[] } | { type: 'directory' };
 
@@ -20,6 +20,11 @@ tasksRouter.get('/', async (ctx) => {
   return ctx.json(tasks);
 });
 
+// Must be declared before '/:name', which would otherwise match "categories".
+tasksRouter.get('/categories', async (ctx) => {
+  return ctx.json(await readCategoryOrder());
+});
+
 tasksRouter.get('/:name', async (ctx) => {
   const name = ctx.req.param('name');