feat: add password confirmation to register + fix i18n hardcoded strings

- Add confirmPassword field to registration form with Zod validation
- Replace ~30 hardcoded French/English strings in admin-settings-form
  with proper t() i18n calls (Ollama models, Custom models, search test)
- Extract SettingsHeader to client component for i18n support
- Add 15 i18n keys to all 15 locale files (auth + admin.ai + admin.tools)
- Remove debug "Config value" line from embeddings section

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/locales/en.json

@@ -26,7 +26,9 @@
     "sending": "Sending...",
     "sendResetLink": "Send Reset Link",
     "backToLogin": "Back to login",
-    "signOut": "Sign out"
+    "signOut": "Sign out",
+    "confirmPassword": "Confirm Password",
+    "confirmPasswordPlaceholder": "Confirm your password"
   },
   "sidebar": {
     "notes": "Notes",
@@ -721,7 +723,17 @@
       "providerCustomOption": "🔧 Custom OpenAI-Compatible",
       "bestValue": "Best value",
       "bestQuality": "Best quality",
-      "saved": "(Saved)"
+      "saved": "(Saved)",
+      "fetchModelsFailed": "Failed to fetch models",
+      "refreshModels": "Refresh Models",
+      "configured": "Configured",
+      "fetchingModels": "Fetching models...",
+      "clickToLoadModels": "Click ↺ to load models",
+      "searchModel": "Search model...",
+      "noModels": "No models. Click ↺",
+      "modelsAvailable": "{count} model(s) available",
+      "enterUrlToLoad": "Enter URL and click ↺ to load models",
+      "currentProvider": "(Current: {provider})"
     },
     "resend": {
       "title": "Resend (Recommended)",
@@ -859,8 +871,11 @@
       "jinaKeyDescription": "Used for web scraping. Works without a key but with rate limits.",
       "saveSettings": "Save Tools Settings",
       "updateSuccess": "Tools settings updated successfully",
-      "updateFailed": "Failed to update tools settings"
-    }
+      "updateFailed": "Failed to update tools settings",
+      "testing": "Testing...",
+      "testSearch": "Test web search"
+    },
+    "settingsDescription": "Configure application-wide settings"
   },
   "about": {
     "title": "About",