fix(shared-help): harden help system with XSS protection, i18n, type safety, and reference implementation

- Add HTML sanitization via isomorphic-dompurify in parser layer to prevent XSS
- Replace all hardcoded English strings with translations (FAQSection, KeyboardShortcuts, ChangelogEntry/Section)
- Remove unsafe `as` type casting in loader.ts, use Zod-inferred generics instead
- Add error logging in content loader (replaces silent catch blocks)
- Fix HelpSearch blur handling (mousedown+preventDefault instead of setTimeout hack)
- Add ARIA attributes to HelpSearch for accessibility
- Derive FAQ categories from items instead of hardcoding all 6
- Fix null-safety in GettingStartedGuide.svelte
- Fix unused appId variable in HelpPage.svelte, add scroll-reset on tab switch
- Rebuild Contacts help page as reference implementation using shared HelpPage component
- Add README with quick-start guide, props docs, and translations template

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

packages/shared-help-content/src/index.ts

@@ -28,6 +28,9 @@ export {
 // Content merger
 export { mergeContent, createEmptyContent } from './merger.js';
 
+// Sanitization
+export { sanitizeHtml } from './sanitize.js';
+
 // Search functionality
 export { buildSearchIndex, search, createSearcher, flattenContentForSearch } from './search.js';