Keep the page you're on in the address

Each page has an address (#filament, #printers, #collection/12), so a refresh
or bookmark returns to it and Back/Forward move between pages. The search
and filter bar is hidden on the Filament page, where it did nothing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

public/app.js

@@ -71,6 +71,7 @@ function startApp() {
   document.getElementById('authScreen').style.display = 'none';
   document.querySelector('.container').style.display = '';
   if (!appStarted) { setupEventListeners(); appStarted = true; }
+  selectedScope = scopeFromHash();
   loadData();
 }
 
@@ -460,8 +461,9 @@ function scopeTitle() {
 }
 
 function updateScopeChrome() {
+  syncAddress(); // e.g. a deleted collection falling back to All Models
   contentTitle.textContent = scopeTitle();
-  const panel = ['duplicates', 'ai', 'watch', 'printers'].includes(selectedScope); // pages without the model grid
+  const panel = ['duplicates', 'ai', 'watch', 'filament', 'printers'].includes(selectedScope); // pages without the model grid
   document.getElementById('filterBar').hidden = panel;
   document.querySelector('.view-options').hidden = panel;
   emptyTrashBtn.hidden = !(selectedScope === 'trash' && trashModels.length);
@@ -977,12 +979,40 @@ function setupEventListeners() {
   document.getElementById('addFilesInput').addEventListener('change', handleAddFiles);
 }
 
-async function selectScope(scope) {
+// The page you're on lives in the address — #filament, #collection/12 — so a
+// refresh or a bookmark comes back to it, and Back and Forward move between pages.
+function scopeHash(scope) {
+  if (scope === 'all') return '';
+  return SPECIAL_SCOPES.includes(scope) ? `#${scope}` : `#collection/${scope}`;
+}
+
+function scopeFromHash() {
+  const h = decodeURIComponent(location.hash.slice(1));
+  const collection = h.match(/^collection\/(\d+)$/);
+  if (collection) return collection[1];
+  return SPECIAL_SCOPES.includes(h) ? h : 'all';
+}
+
+// Keeps the address in step with the page shown; `push` makes a Back step.
+function syncAddress(push = false) {
+  const hash = scopeHash(String(selectedScope));
+  if (location.hash === hash || (!hash && !location.hash)) return;
+  history[push ? 'pushState' : 'replaceState'](null, '', `${location.pathname}${location.search}${hash}`);
+}
+
+async function selectScope(scope, { push = true } = {}) {
   selectedScope = scope;
+  syncAddress(push);
   if (scope === 'trash') await loadTrash();
   renderModels();
 }
 
+window.addEventListener('popstate', () => {
+  if (!appStarted) return;
+  const scope = scopeFromHash();
+  if (String(scope) !== String(selectedScope)) selectScope(scope, { push: false });
+});
+
 // Tracks the file currently shown in the detail viewer (for thumbnail regen).
 let currentDetailFile = null;
 let currentDetailThumb = null; // model image, used as a viewer fallback