fix(mobile): render notes with marked (proper Markdown→HTML) + design CSS soigné

- Install marked package (UMD, hors-ligne)
- buildHtml: parse Markdown server-side avec marked, inject HTML statique
- CSS: typographie soignée, blockquotes brandés, code dark, tables propres
- Plus de CDN, fonctionne hors-ligne

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

memento-mobile/package-lock.json

@@ -18,6 +18,7 @@
         "expo-splash-screen": "~31.0.13",
         "expo-status-bar": "~3.0.9",
         "lucide-react-native": "^0.477.0",
+        "marked": "^18.0.4",
         "react": "19.1.0",
         "react-native": "0.81.5",
         "react-native-safe-area-context": "~5.6.0",
@@ -6225,6 +6226,18 @@
         "tmpl": "1.0.5"
       }
     },
+    "node_modules/marked": {
+      "version": "18.0.4",
+      "resolved": "https://registry.npmjs.org/marked/-/marked-18.0.4.tgz",
+      "integrity": "sha512-c/BTaKzg0G6ezQx97DAkYU7k0HM6ys0FqYeKBL6hlBByZwy+ycA1+f0vDdjMHKKeEjdgkx0GOv9Il6D+85cOqA==",
+      "license": "MIT",
+      "bin": {
+        "marked": "bin/marked.js"
+      },
+      "engines": {
+        "node": ">= 20"
+      }
+    },
     "node_modules/marky": {
       "version": "1.3.0",
       "resolved": "https://registry.npmjs.org/marky/-/marky-1.3.0.tgz",