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-ui/src/pages/HelpPage.svelte

@@ -12,7 +12,7 @@
 	let {
 		content,
 		appName,
-		appId: _appId,
+		appId,
 		translations,
 		searchEnabled = true,
 		showFAQ = true,
@@ -57,9 +57,13 @@
 
 	const visibleSections = $derived(sections.filter((s) => s.show));
 
+	let contentRef: HTMLDivElement;
+
 	function setActiveSection(section: HelpSection) {
 		activeSection = section;
 		onSectionChange?.(section);
+		// Scroll content area into view on tab change
+		contentRef?.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
 	}
 
 	function handleSearchResultSelect(result: SearchResult) {
@@ -151,7 +155,7 @@
 	{/if}
 
 	<!-- Content -->
-	<div class="min-h-[400px]">
+	<div class="min-h-[400px]" bind:this={contentRef}>
 		{#if activeSection === 'faq' && showFAQ}
 			<FAQSection items={content.faq} {translations} expandFirst />
 		{:else if activeSection === 'features' && showFeatures}