feat: Add Manage page, light/dark theme toggle, and URL sharing

- Move Save, Load, Export, Import buttons to a dedicated Manage page
- Add light theme with warm parchment palette; auto-detect via prefers-color-scheme, persisted to localStorage
- Add URL sharing: sheet state is deflate-raw compressed, base64-encoded, and stored in ?c= parameter; auto-save is suppressed when viewing a shared URL
- Extract JS to fabula-ultima-sheet.js

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fabula-ultima-sheet.js

@@ -1,4 +1,5 @@
 // ── STATE ──────────────────────────────────────────
+let urlMode = false;
 let level = 1;
 let fpCount = 0;
 let primaryClasses = [];
@@ -25,7 +26,7 @@ function switchTab(tab) {
 }
 
 // ── INIT ───────────────────────────────────────────
-function init() {
+async function init() {
   const savedTheme = localStorage.getItem('fabulaUltimaTheme')
     || (window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark');
   document.getElementById('themeToggle').textContent = savedTheme === 'light' ? '☾ Dark' : '☀ Light';
@@ -36,7 +37,50 @@ function init() {
   renderOtherClasses();
   renderSpells();
   updateXPBar();
-  tryAutoLoad();
+  if (!await tryLoadFromURL()) tryAutoLoad();
+}
+
+// ── URL STATE ──────────────────────────────────────
+async function compressToBase64(str) {
+  const stream = new CompressionStream('deflate-raw');
+  const writer = stream.writable.getWriter();
+  writer.write(new TextEncoder().encode(str));
+  writer.close();
+  const buf = await new Response(stream.readable).arrayBuffer();
+  const bytes = new Uint8Array(buf);
+  let binary = '';
+  for (let i = 0; i < bytes.length; i++) binary += String.fromCharCode(bytes[i]);
+  return btoa(binary);
+}
+
+async function decompressFromBase64(b64) {
+  try {
+    const bytes = Uint8Array.from(atob(b64), c => c.charCodeAt(0));
+    const stream = new DecompressionStream('deflate-raw');
+    const writer = stream.writable.getWriter();
+    writer.write(bytes);
+    writer.close();
+    const buf = await new Response(stream.readable).arrayBuffer();
+    return new TextDecoder().decode(buf);
+  } catch {
+    // Fall back to legacy uncompressed URLs
+    return decodeURIComponent(escape(atob(b64)));
+  }
+}
+
+async function tryLoadFromURL() {
+  const encoded = new URLSearchParams(window.location.search).get('c');
+  if (!encoded) return false;
+  try {
+    const json = await decompressFromBase64(encoded);
+    applyData(JSON.parse(json));
+    urlMode = true;
+    document.getElementById('urlBanner').style.display = 'block';
+    return true;
+  } catch (e) {
+    console.warn('Could not load state from URL:', e);
+    return false;
+  }
 }
 
 // ── STATUS EFFECTS ─────────────────────────────────
@@ -236,7 +280,8 @@ function collectData() {
   };
 }
 
-function saveSheet() {
+function saveSheet(isAuto = false) {
+  if (isAuto && urlMode) return;
   const data = collectData();
   localStorage.setItem('fabulaUltimaSheet', JSON.stringify(data));
   const st = document.getElementById('saveStatus');
@@ -350,6 +395,16 @@ function handleImportFile(input) {
   reader.readAsText(file);
 }
 
+async function copyShareURL() {
+  const json = JSON.stringify(collectData());
+  const encoded = await compressToBase64(json);
+  const url = window.location.origin + window.location.pathname + '?c=' + encodeURIComponent(encoded);
+  await navigator.clipboard.writeText(url);
+  const st = document.getElementById('copyStatus');
+  st.classList.add('show');
+  setTimeout(() => st.classList.remove('show'), 2000);
+}
+
 // ── THEME ──────────────────────────────────────────
 function toggleTheme() {
   const html = document.documentElement;
@@ -360,6 +415,6 @@ function toggleTheme() {
 }
 
 // Auto-save every 30s
-setInterval(saveSheet, 30000);
+setInterval(() => saveSheet(true), 30000);
 
 init();