Remove experimental allowed domains feature (#697)

* chore: remove experimental allowed domains feature

Remove the experimental_allowed_domains feature which was used to
restrict network access via a Squid proxy. This removes:

- The input definition from action.yml
- The Network Restrictions workflow step
- The setup-network-restrictions.sh script
- Documentation from experimental.md, usage.md, and related files
- The input default from collect-inputs.ts

* chore: fix formatting with prettier

Co-authored-by: Ashwin Bhat <ashwin-ant@users.noreply.github.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Ashwin Bhat <ashwin-ant@users.noreply.github.com>

src/entrypoints/collect-inputs.ts

@@ -26,7 +26,6 @@ export function collectActionInputsPresence(): void {
     max_turns: "",
     use_sticky_comment: "false",
     use_commit_signing: "false",
-    experimental_allowed_domains: "",
   };
 
   const allInputsJson = process.env.ALL_INPUTS;