fix(audit): nettoyage accès, garde-fous build, unification quotas

Semaine 1 — fuites et accès :
- /archive rendu accessible via sidebar (était invisible)
- Suppression pages orphelines : /chat, /graph, /support, test-title-suggestions
- Fixes i18n : search-modal (clé non interpolée), sidebar tooltips, export PDF
- 15 locales mises à jour

Semaine 2 — garde-fous :
- 8 erreurs TS fixees → ignoreBuildErrors: false (build type-safe)
- reactStrictMode: true (dev-only, zero impact prod)
- reserveUsageOrThrow → wrapper deprecie vers reserveAiUsageOrThrow
- auth-guard.ts : requireAuthOrResponse() + requireAdminOrResponse()

Tests 212/212 | Lint 0 erreur | Build OK | tsc 0 erreur

memento-note/locales/de.json

@@ -3318,10 +3318,8 @@
         "title": "Konto",
         "link0": "Anmelden",
         "link1": "Registrieren",
-        "link2": "Support",
         "link0Href": "/login",
-        "link1Href": "/register",
-        "link2Href": "/support"
+        "link1Href": "/register"
       },
       "legal": {
         "title": "Rechtliches",
@@ -3685,7 +3683,8 @@
     "typeForResults": "Tippen für sofortige Ergebnisse.",
     "hintNavigate": "navigieren",
     "hintOpen": "öffnen",
-    "hintClose": "schließen"
+    "hintClose": "schließen",
+    "selectResultToPreview": "Select a result to explore its content."
   },
   "quotaPaywall": {
     "title": "Monatliches Limit erreicht",