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/db/schema.sql

@@ -28,15 +28,34 @@ CREATE TABLE IF NOT EXISTS posts (
   INDEX idx_posts_feed (category, published, published_at)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 
+-- Wiki categories / sections. Defined before wiki_pages so the FK resolves on a
+-- fresh install. Pages reference a category (nullable = "Uncategorized").
+CREATE TABLE IF NOT EXISTS wiki_categories (
+  id          INT AUTO_INCREMENT PRIMARY KEY,
+  slug        VARCHAR(120) NOT NULL UNIQUE,
+  title       VARCHAR(200) NOT NULL,
+  description VARCHAR(400) NULL,
+  sort_order  INT NOT NULL DEFAULT 0,
+  created_at  DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at  DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
 CREATE TABLE IF NOT EXISTS wiki_pages (
-  id         INT AUTO_INCREMENT PRIMARY KEY,
-  slug       VARCHAR(120) NOT NULL UNIQUE,
-  title      VARCHAR(200) NOT NULL,
-  body       MEDIUMTEXT   NULL,
-  updated_by INT NULL,
-  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
-  updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-  CONSTRAINT fk_wiki_user FOREIGN KEY (updated_by) REFERENCES users(id) ON DELETE SET NULL
+  id           INT AUTO_INCREMENT PRIMARY KEY,
+  slug         VARCHAR(120) NOT NULL UNIQUE,
+  title        VARCHAR(200) NOT NULL,
+  body         MEDIUMTEXT   NULL,
+  excerpt      VARCHAR(400) NULL,
+  category_id  INT NULL,
+  published    TINYINT(1)   NOT NULL DEFAULT 1,
+  sort_order   INT NOT NULL DEFAULT 0,
+  updated_by   INT NULL,
+  created_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  published_at DATETIME NULL,
+  CONSTRAINT fk_wiki_user FOREIGN KEY (updated_by) REFERENCES users(id) ON DELETE SET NULL,
+  CONSTRAINT fk_wiki_category FOREIGN KEY (category_id) REFERENCES wiki_categories(id) ON DELETE SET NULL,
+  FULLTEXT INDEX idx_wiki_search (title, body)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 
 CREATE TABLE IF NOT EXISTS settings (
@@ -57,3 +76,15 @@ CREATE TABLE IF NOT EXISTS activity_log (
   CONSTRAINT fk_activity_user FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE SET NULL,
   INDEX idx_activity_created (created_at)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+-- Migrations for databases created before the wiki upgrade. Each statement uses
+-- IF NOT EXISTS so re-running on every boot is a harmless no-op. New installs get
+-- these columns from the CREATE TABLE above; existing installs get them here.
+-- (The category foreign key is only added on fresh installs; on upgraded databases
+-- referential integrity for category_id is enforced in application code.)
+ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS excerpt VARCHAR(400) NULL;
+ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS category_id INT NULL;
+ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS published TINYINT(1) NOT NULL DEFAULT 1;
+ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS sort_order INT NOT NULL DEFAULT 0;
+ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS published_at DATETIME NULL;
+ALTER TABLE wiki_pages ADD FULLTEXT INDEX IF NOT EXISTS idx_wiki_search (title, body);