docs: correct DOKPLOY_REDACT_ENV default in .env.example

The README already documents the default as true and clientConfig.ts reads
it with parseBoolean(..., true), but .env.example still said "Off by
default" and suggested setting it to true. Align the example with the
actual behaviour so readers do not assume redaction is opt-in.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
(cherry picked from commit de2cee800158e23dea8be803fb3784931a31cb86)