[grade=A] DC-065: Sweep 15 console.* calls to process.stderr.write

Replace all non-logger console.error/warn calls with process.stderr.write
using tagged prefixes ([AuditLogger], [CSRF], [DNS Registry], etc.) for
grep-ability. All in fallback/catch paths where structured logger may be
unavailable. Test updated to use jest.spyOn with try/finally for clean
mock restoration.

Codex grade: pass (22,402 tokens). All 1539 tests pass.

dashcaddy-api/src/auth/providers/email.js

@@ -410,8 +410,7 @@ class EmailMagicLinkProvider extends AuthProvider {
     if (this.deps.log && typeof this.deps.log.warn === 'function') {
       this.deps.log.warn('auth-magic-dev', marker);
     } else {
-      // eslint-disable-next-line no-console
-      console.warn(marker);
+      process.stderr.write(`${marker}\n`);
     }
   }