Convert backend from submodule to regular directory

Remove submodule tracking; backend is now a plain directory in the repo.
Also update deploy workflow: remove --recurse-submodules.

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

backend/internal/api/static/day.js

@@ -0,0 +1,47 @@
+// GPS button
+document.getElementById('btn-gps')?.addEventListener('click', function () {
+  const status = document.getElementById('gps-status');
+  if (!navigator.geolocation) {
+    status.textContent = '// GPS nicht verfügbar';
+    return;
+  }
+  status.textContent = '// Standort wird ermittelt...';
+  navigator.geolocation.getCurrentPosition(
+    function (pos) {
+      document.getElementById('entry-lat').value = pos.coords.latitude.toFixed(6);
+      document.getElementById('entry-lon').value = pos.coords.longitude.toFixed(6);
+      status.textContent = '// Standort gesetzt (' + pos.coords.accuracy.toFixed(0) + ' m Genauigkeit)';
+    },
+    function (err) {
+      status.textContent = '// Fehler: ' + err.message;
+    },
+    { enableHighAccuracy: true, timeout: 10000 }
+  );
+});
+
+// Set current time as default
+(function () {
+  const input = document.getElementById('entry-time');
+  if (input && !input.value) {
+    const now = new Date();
+    const hh = String(now.getHours()).padStart(2, '0');
+    const mm = String(now.getMinutes()).padStart(2, '0');
+    input.value = hh + ':' + mm;
+  }
+})();
+
+// Image preview
+document.getElementById('image-input')?.addEventListener('change', function () {
+  const preview = document.getElementById('image-preview');
+  preview.innerHTML = '';
+  Array.from(this.files).forEach(function (file) {
+    if (!file.type.startsWith('image/')) return;
+    const reader = new FileReader();
+    reader.onload = function (e) {
+      const img = document.createElement('img');
+      img.src = e.target.result;
+      preview.appendChild(img);
+    };
+    reader.readAsDataURL(file);
+  });
+});