feat(pos): add exploded diagrams feature (#9) with interactive SVG viewer

- Blueprint with API endpoints: list, detail, SVG serve, vehicle-linked diagrams
- Interactive SVG viewer with zoom/pan (mouse wheel, drag, touch, keyboard)
- Clickable hotspots that highlight on hover and show part detail panel
- Parts sidebar listing all callout numbers with catalog search integration
- 3 placeholder SVG diagrams: braking system, suspension, engine components
- Seeded diagrams, hotspots, and vehicle_diagrams in DB
- Added to sidebar nav, i18n (ES/EN), and "Ver diagramas" link in catalog

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/static/js/catalog.js

@@ -122,7 +122,7 @@
     }
 
     // ─── UI helpers ───
-    function showLoading() { loading.classList.add('is-visible'); navGrid.innerHTML = ''; partsGrid.style.display = 'none'; partsGrid.innerHTML = ''; emptyState.classList.remove('is-visible'); paginationNav.innerHTML = ''; }
+    function showLoading() { loading.classList.add('is-visible'); navGrid.innerHTML = ''; partsGrid.style.display = 'none'; partsGrid.innerHTML = ''; emptyState.classList.remove('is-visible'); paginationNav.innerHTML = ''; var dl = document.getElementById('diagLink'); if (dl && nav.level !== 'categories') dl.style.display = 'none'; }
     function hideLoading() { loading.classList.remove('is-visible'); }
 
     function showEmpty(title, subtitle) {
@@ -345,6 +345,19 @@
         updateBreadcrumb();
         levelTitle.textContent = 'Categorias de partes';
         setupLevelFilter(true);
+        // Add "Ver diagramas" link
+        var diagLink = document.getElementById('diagLink');
+        if (!diagLink) {
+            diagLink = document.createElement('a');
+            diagLink.id = 'diagLink';
+            diagLink.href = '/pos/diagrams';
+            diagLink.className = 'btn-diagram-link';
+            diagLink.innerHTML = '<svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14.7 6.3a1 1 0 000 1.4l1.6 1.6a1 1 0 001.4 0l3.77-3.77a6 6 0 01-7.94 7.94l-6.91 6.91a2.12 2.12 0 01-3-3l6.91-6.91a6 6 0 017.94-7.94l-3.76 3.76z"/></svg> Ver diagramas';
+            diagLink.style.cssText = 'display:inline-flex;align-items:center;gap:6px;padding:6px 14px;background:var(--color-primary-muted);color:var(--color-primary);border:1px solid var(--color-primary);border-radius:var(--radius-md);font-size:var(--text-body-sm);font-weight:600;text-decoration:none;cursor:pointer;transition:var(--transition-fast);margin-left:auto;';
+            var titleContainer = levelTitle.parentElement;
+            if (titleContainer) titleContainer.appendChild(diagLink);
+        }
+        diagLink.style.display = 'inline-flex';
         showLoading();
 
         apiFetch(API + '/categories?mye_id=' + nav.engine.id_mye).then(function (data) {