feat(mindspace): add achievements showcase with paginated management

Ship the M成果 page with list/delete UX, fix deletePage for incomplete page records, route /space/achievements, and add M成果 under the WeChat M空间 menu.

Co-authored-by: Cursor <cursoragent@cursor.com>

mindspace-page-achievement-list.test.mjs

@@ -0,0 +1,11 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { parseAchievementQuery } from './mindspace-page-achievement-list.mjs';
+
+test('parseAchievementQuery defaults to fast paginated listing', () => {
+  const parsed = parseAchievementQuery({});
+  assert.equal(parsed.limit, 20);
+  assert.equal(parsed.offset, 0);
+  assert.equal(parsed.includeStats, false);
+});