slice 2 UI: 2FA enrollment (enable -> secret/QR/backup codes -> confirm)

Orchestrator (me) SPA work: auth client +2FA/OAuth methods, 2FA strings, AuthSection
enrollment flow. Primary-Rule lint stays green. Slice 2 (auth-2fa-and-social-oauth)
COMPLETE: 2FA + OAuth backend (ornith modules + me integration) + 2FA enrollment UI.

app/src/lib/strings.ts

@@ -24,6 +24,15 @@ export const UI_STRINGS = {
   loginButton: "Sign in",
   logoutButton: "Sign out",
   signupPrompt: "Create an account to track symbols and keep your research in one place.",
+  enable2faButton: "Enable two-factor",
+  twoFactorSecretLabel: "Two-factor secret (base32)",
+  twoFactorQrLabel: "Scan this in an authenticator app, or enter the secret manually.",
+  backupCodesLabel: "Backup codes — store these somewhere safe.",
+  confirm2faButton: "Confirm with a code",
+  twoFactorCodePlaceholder: "6-digit code",
+  twoFactorEnabled: "Two-factor is now enabled. Login will ask for a code.",
+  oauthGithub: "Continue with GitHub",
+  oauthGoogle: "Continue with Google",
 } as const;
 
 export const UI_STRING_LIST: string[] = Object.values(UI_STRINGS);