Wiki Phase 1: categories, drafts/publish, HTML sanitization

Foundation & safety phase of the wiki upgrade (see WIKI_UPGRADE.md).

Schema (additive, idempotent via ensureSchema):
- new wiki_categories table; wiki_pages gains category_id, excerpt,
  published, published_at, sort_order, and a FULLTEXT index
- migration ALTERs guarded with IF NOT EXISTS for existing databases
- seed reworked into 4 sections with the 8 starter pages assigned

Security:
- new utils/sanitizeHtml.js (sanitize-html allowlist); wiki bodies are
  sanitized on every save, and the article renders through DOMPurify
- strips <script>, event handlers (onerror), and javascript: URLs

Backend:
- public: published-only list with ?category filter + /wiki/categories
- admin: extended page CRUD, PATCH publish toggle, category CRUD;
  drafts visible to admin, hidden from public
- all writes logged to activity_log

Frontend:
- data-driven public wiki index (sections + real descriptions; removed
  hardcoded blurbs/Roman numerals) with ?category filtering
- article: category breadcrumb + sanitized render
- admin: Section/Status columns, draft/publish + section + excerpt in the
  editor, and a Manage sections modal

Verified end-to-end against MariaDB 11: migration clean, XSS neutralized,
drafts hidden, client builds, server boots.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/router/v1/public/public.routes.js

@@ -25,6 +25,8 @@ publicRouter.post(
 publicRouter.get('/posts/:category', siteMode, ctrl.getPosts)
 publicRouter.get('/posts/:category/:idOrSlug', siteMode, ctrl.getPost)
 publicRouter.get('/wiki', siteMode, ctrl.getWikiList)
+// Static path must precede the :slug route so it isn't captured as a slug.
+publicRouter.get('/wiki/categories', siteMode, ctrl.getWikiCategories)
 publicRouter.get('/wiki/:slug', siteMode, ctrl.getWikiPage)
 
 module.exports = publicRouter