feat: Add manual OAuth authorization mode for WebUI (#131)

* feat: add manual OAuth flow support in WebUI

* fix: reset add account modal state on close

* feat: display custom API key in startup banner

* fix: move translations to separate files and optimize import API

* fix: remove orphaned model-manager.js and cleanup callback server on manual auth

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Co-authored-by: Badri Narayanan S <59133612+badrisnarayanan@users.noreply.github.com>

public/js/translations/id.js

@@ -337,6 +337,24 @@ window.translations.id = {
     quotaDistribution: "Distribusi Kuota",
     resetsIn: "Reset dalam {time}",
     noQuotaData: "Data kuota belum tersedia untuk akun ini.",
+    // Manual OAuth Mode
+    manualMode: "Mode Manual",
+    manualModeDesc: "(untuk lingkungan di mana callback tidak bisa dicapai)",
+    authLinkLabel: "Link Otorisasi:",
+    linkCopied: "Link disalin ke clipboard",
+    pasteCallbackLabel: "Tempel callback URL atau kode:",
+    pasteCallbackPlaceholder: "http://localhost:51121/oauth-callback?code=... atau 4/0xxx...",
+    completeAuth: "Selesaikan Otorisasi",
+    authFailed: "Otorisasi gagal",
+    // Import/Export
+    export: "Ekspor",
+    import: "Impor",
+    exportAccounts: "Ekspor Akun",
+    importAccounts: "Impor Akun",
+    exportSuccess: "Berhasil mengekspor {count} akun",
+    exportFailed: "Gagal mengekspor",
+    importSuccess: "Impor selesai:",
+    importFailed: "Gagal mengimpor",
 
     // Completed TODOs
     pageTitle: "Antigravity Console",