feat: plugin analytics avec custom field kirbyup + Chart.js

Refactoring complet du plugin analytics : remplacement de la section
avec template Vue inline par un custom field compilé avec kirbyup.
Dashboard avec KPIs, line chart Chart.js et filtres par date.

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

public/site/plugins/analytics/package-lock.json

@@ -0,0 +1,30 @@
+{
+  "name": "analytics",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "dependencies": {
+        "chart.js": "^4.4.0"
+      }
+    },
+    "node_modules/@kurkle/color": {
+      "version": "0.3.4",
+      "resolved": "https://registry.npmjs.org/@kurkle/color/-/color-0.3.4.tgz",
+      "integrity": "sha512-M5UknZPHRu3DEDWoipU6sE8PdkZ6Z/S+v4dD+Ke8IaNlpdSQah50lz1KtcFBa2vsdOnwbbnxJwVM4wty6udA5w==",
+      "license": "MIT"
+    },
+    "node_modules/chart.js": {
+      "version": "4.5.1",
+      "resolved": "https://registry.npmjs.org/chart.js/-/chart.js-4.5.1.tgz",
+      "integrity": "sha512-GIjfiT9dbmHRiYi6Nl2yFCq7kkwdkp1W/lp2J99rX0yo9tgJGn3lKQATztIjb5tVtevcBtIdICNWqlq5+E8/Pw==",
+      "license": "MIT",
+      "dependencies": {
+        "@kurkle/color": "^0.3.0"
+      },
+      "engines": {
+        "pnpm": ">=8"
+      }
+    }
+  }
+}