Add line wrap toggle for editor and paste viewer (#130)

Shared client-side preference in localStorage 'palette-wrap', default
off. Toggle button on /new editor head and paste title bar, plus a Line
wrap checkbox in the settings menu; all read/write the same preference.
Active state uses the accent treatment like other toggles. No em dashes
in UI text.

internal/web/templates/layout.html

@@ -46,6 +46,37 @@
   // do not persist anything here: URL theme is a one-off override
   document.documentElement.dataset.preset = dark ? PAIRS[t].dark : PAIRS[t].light;
 })();
+// #130: shared line wrap preference (localStorage 'palette-wrap', default off)
+(function () {
+  function wrapOn() {
+    try { return localStorage.getItem('palette-wrap') === '1'; } catch (e) { return false; }
+  }
+  function wrapApply(on) {
+    if (on) document.documentElement.setAttribute('data-wrap', '1');
+    else document.documentElement.removeAttribute('data-wrap');
+    document.querySelectorAll('.wrap-toggle').forEach(function (b) {
+      b.setAttribute('aria-pressed', on ? 'true' : 'false');
+    });
+    var s = document.getElementById('wrap-setting');
+    if (s) s.checked = on;
+  }
+  window.paletteWrapToggle = function () {
+    var on = !wrapOn();
+    try { localStorage.setItem('palette-wrap', on ? '1' : '0'); } catch (e) {}
+    wrapApply(on);
+    return on;
+  };
+  document.addEventListener('DOMContentLoaded', function () {
+    wrapApply(wrapOn());
+    document.querySelectorAll('.wrap-toggle').forEach(function (b) {
+      b.addEventListener('click', function () { window.paletteWrapToggle(); });
+    });
+    var s = document.getElementById('wrap-setting');
+    if (s) s.addEventListener('change', function () {
+      if (s.checked !== wrapOn()) window.paletteWrapToggle();
+    });
+  });
+})();
 </script>
 {{end}}