Add Wiki feature with Markdown, categories, tags, and search

- wiki_categories, wiki_pages, wiki_tags, wiki_page_tags tables
- /wiki overview with category-grouped pages, tag sidebar, search
- /wiki/new create page with Markdown editor and live preview
- /wiki/[slug] view page with rendered Markdown, tags, edit/delete
- /wiki/[slug]/edit with pre-populated editor
- Tag input with existing tag suggestions (click to add)
- Category management (add/delete) in sidebar
- Tailwind Typography plugin for prose styling
- marked package for Markdown rendering
- Sidebar nav item with book icon

Run db:push on server to create wiki tables.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/app.css

@@ -1,3 +1,4 @@
 @import 'tailwindcss';
+@plugin '@tailwindcss/typography';
 
 @custom-variant dark (&:where(.dark, .dark *));