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/en.js

@@ -298,6 +298,24 @@ window.translations.en = {
     quotaDistribution: "Quota Distribution",
     resetsIn: "Resets in {time}",
     noQuotaData: "No quota data available for this account yet.",
+    // Manual OAuth Mode
+    manualMode: "Manual Mode",
+    manualModeDesc: "(for environments where callback cannot reach)",
+    authLinkLabel: "Authorization Link:",
+    linkCopied: "Link copied to clipboard",
+    pasteCallbackLabel: "Paste callback URL or code:",
+    pasteCallbackPlaceholder: "http://localhost:51121/oauth-callback?code=... or 4/0xxx...",
+    completeAuth: "Complete Authorization",
+    authFailed: "Authorization failed",
+    // Import/Export
+    export: "Export",
+    import: "Import",
+    exportAccounts: "Export Accounts",
+    importAccounts: "Import Accounts",
+    exportSuccess: "Exported {count} accounts",
+    exportFailed: "Export failed",
+    importSuccess: "Import complete:",
+    importFailed: "Import failed",
     // UI Elements
     pageTitle: "Antigravity Console",
     live: "Live",