feat(js): implement intersection observer lazy loading for adsense

- Add per-slot lazy loading with Intersection Observer API
- Implement fill detection via MutationObserver and data-ad-status
- Add configurable rootMargin and fillTimeout from database
- Generate dynamic CSS based on lazy_loading_enabled setting
- Add legacy mode fallback for browsers without IO support
- Include backup of previous implementation (adsense-loader.legacy.js)
- Add OpenSpec documentation with test plan (72 tests verified)

Schema changes:
- Add lazy_loading_enabled (boolean, default: true)
- Add lazy_rootmargin (select: 0-500px, default: 200)
- Add lazy_fill_timeout (select: 3000-10000ms, default: 5000)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Schemas/adsense-placement.json

@@ -1,6 +1,6 @@
 {
   "component_name": "adsense-placement",
-  "version": "1.4.0",
+  "version": "1.5.0",
   "description": "Control de AdSense y Google Analytics - Con In-Content Ads Avanzado",
   "groups": {
     "visibility": {
@@ -423,6 +423,41 @@
             "700": "700px (Debajo del fold)"
           },
           "description": "Distancia vertical desde el top del viewport"
+        },
+        "lazy_loading_enabled": {
+          "type": "boolean",
+          "label": "Lazy Loading de Anuncios",
+          "default": true,
+          "editable": true,
+          "description": "Cargar anuncios individualmente al entrar al viewport (mejora fill rate)"
+        },
+        "lazy_rootmargin": {
+          "type": "select",
+          "label": "Pre-carga (px antes del viewport)",
+          "default": "200",
+          "editable": true,
+          "options": {
+            "0": "0px (sin pre-carga)",
+            "100": "100px",
+            "200": "200px (recomendado)",
+            "300": "300px",
+            "400": "400px",
+            "500": "500px"
+          },
+          "description": "Pixeles de anticipacion para iniciar carga de anuncio"
+        },
+        "lazy_fill_timeout": {
+          "type": "select",
+          "label": "Timeout de llenado (ms)",
+          "default": "5000",
+          "editable": true,
+          "options": {
+            "3000": "3 segundos",
+            "5000": "5 segundos (recomendado)",
+            "7000": "7 segundos",
+            "10000": "10 segundos"
+          },
+          "description": "Tiempo maximo para esperar contenido de Google antes de ocultar slot"
         }
       }
     },