feat(app-form): icon picker, tag/category autocomplete, typography

- Replace AppIconPicker text input with visual IconPickerButton for
  lucide icons (grid with search)
- Add AutocompleteInput component for category field with existing
  category suggestions
- Add TagsInput component for tags field with tag pills, autocomplete
  from existing tags, and keyboard navigation
- Add GET /api/apps/suggestions endpoint returning all categories/tags
- Add getAllTags() to appService (merges Tag model + comma-separated)
- Install @tailwindcss/typography plugin to fix prose rendering
  (headings, lists, blockquotes now render in Note/Markdown widgets)
- Fix note widget validator test for new html format

src/app.css

@@ -1,5 +1,6 @@
 @import 'tailwindcss';
 @import 'tw-animate-css';
+@plugin '@tailwindcss/typography';
 
 @custom-variant dark (&:is(.dark *));