feat: dynamic page titles + social media meta tags

Browser tab titles:
- Protocol pages: 'Title · Site Name'
- Collection pages: 'Title · Site Name'
- User pages: '@username · Site Name'
- Resets to site name on library/collections/about

Social media previews (server-side, for crawlers):
- index.php detects /protocols/slug, /collections/slug, /users/username
- Looks up title + description from DB
- Injects og:title, og:description, og:type, og:site_name, og:url
- Injects twitter:card, twitter:title, twitter:description
- Replaces default <title> with enriched version

Frontend:
- Default og/twitter meta tags on homepage
- Path-based URLs (shared links) redirect to hash routes for SPA routing

frontend/app.js

@@ -39,6 +39,13 @@ async function api(path, options = {}) {
 
 // --- Init ---
 async function init() {
+  // If path looks like /protocols/slug, /collections/slug, or /users/username
+  // (shared link without hash), redirect to hash-based route
+  var pathMatch = location.pathname.match(/^\/?(protocols|collections|users)\/([^\/]+)/);
+  if (pathMatch && !location.hash) {
+    history.replaceState(null, '', '#' + pathMatch[1] + '/' + pathMatch[2]);
+  }
+
   // Route immediately — don't wait for API calls
   route();
   window.addEventListener('hashchange', route);
@@ -98,6 +105,7 @@ function navigate(view) {
   document.querySelectorAll('.mobile-panel a').forEach(a => a.classList.toggle('active', a.dataset.view === view));
   closeMenu();
   updateBreadcrumb(view);
+  document.title = siteConfig.name || 'Protocol Droid';
   if (!isRouting) {
     if (view === 'library') location.hash = 'library';
     if (view === 'collections') location.hash = 'collections';
@@ -329,6 +337,7 @@ async function showDetail(slug) {
 
   try {
     const p = await api('/protocols/' + slug);
+    document.title = (p.title || slug) + ' · ' + (siteConfig.name || 'Protocol Droid');
     document.getElementById('detailContent').innerHTML = renderDetail(p);
     renderDetailActions(p);
   } catch (e) {
@@ -730,6 +739,7 @@ async function showCollectionDetail(slug) {
 
   try {
     var c = await api('/collections/' + slug);
+    document.title = (c.title || slug) + ' · ' + (siteConfig.name || 'Protocol Droid');
     var itemsHtml = '';
     for (var i = 0; i < (c.items || []).length; i++) {
       var item = c.items[i];
@@ -802,6 +812,7 @@ async function showUser(username) {
   closeMenu();
   try {
     const data = await api('/users/' + username);
+    document.title = '@' + (data.user.display_name || data.user.username) + ' · ' + (siteConfig.name || 'Protocol Droid');
     const p = data.protocols || [];
     const c = data.collections || [];
     document.getElementById('detailContent').innerHTML =