docs(cloudflare): add DO worker setup for skew protection

[alex-all3dp]

@vicb I added a new section to the skew protection page explaining how to use Durable Object-based overrides (doShardedTagCache, doQueue, purgeCache) together with skew protection.

The existing skew protection docs state that DOs need to be in a separate worker, but don't explain the setup in detail. This added section covers:

• The DO worker entry point that re-exports the DO classes
• Wrangler configs for both workers (script_name bindings in the main worker, WORKER_SELF_REFERENCE in the DO worker)
• The bootstrap deploy pattern to break the circular dependency on a fresh environment

I hope this aligns with the multi-worker setup you were referencing in your initial answer. Happy to adjust it further of course or learn about possible shortcomings in the path we chose.

Closes opennextjs/opennextjs-cloudflare#834