feat: implementar 12 mejoras, tests, docs y optimizaciones

- Fase A: license templates, search history, cost estimator
- Fase B: import URL, bulk ZIP, batch download
- Fase C: comparison mode, mesh validation, measurement tool
- Fase D: cross-section clipping, overhang heatmap, layer animation
- Refactor Pydantic/SQLAlchemy warnings
- 24 tests pytest
- README actualizado
- WebP thumbnails, lazy loading, cache headers

static/js/api.js

@@ -0,0 +1,59 @@
+const API_BASE = '/api';
+
+function showToast(message, type = 'info') {
+  const container = document.getElementById('toast-container');
+  if (!container) return;
+  const toast = document.createElement('div');
+  toast.className = `toast ${type}`;
+  toast.textContent = message;
+  container.appendChild(toast);
+  setTimeout(() => {
+    toast.style.opacity = '0';
+    toast.style.transform = 'translateX(20px)';
+    toast.style.transition = 'all 0.3s ease';
+    setTimeout(() => toast.remove(), 300);
+  }, 4000);
+}
+
+async function apiGet(path) {
+  const res = await fetch(API_BASE + path);
+  if (!res.ok) {
+    const text = await res.text();
+    throw new Error(text || `HTTP ${res.status}`);
+  }
+  return res.json();
+}
+
+async function apiDelete(path) {
+  const res = await fetch(API_BASE + path, { method: 'DELETE' });
+  if (!res.ok) {
+    const text = await res.text();
+    throw new Error(text || `HTTP ${res.status}`);
+  }
+  return res.json();
+}
+
+async function apiPostForm(path, formData) {
+  const res = await fetch(API_BASE + path, {
+    method: 'POST',
+    body: formData,
+  });
+  if (!res.ok) {
+    const text = await res.text();
+    throw new Error(text || `HTTP ${res.status}`);
+  }
+  return res.json();
+}
+
+async function apiPut(path, data) {
+  const res = await fetch(API_BASE + path, {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(data),
+  });
+  if (!res.ok) {
+    const text = await res.text();
+    throw new Error(text || `HTTP ${res.status}`);
+  }
+  return res.json();
+}