ci: publish Packages for Package API v4

[Mathih13]

Core now requires Package API v4, but the Official Package Collection still checks a v3 Core revision. Its publication job therefore never creates api-v4, and Package updates refuse to run.

Pin the compatibility and playerbots workflows to merged Core ca0a49e4. Update the collection README to declare v4. The existing publication job will create api-v4 after the required checks pass on main. Older API tags stay unchanged.

Tag-publication tests and the artifact firewall pass locally. The Core compatibility check passes against ca0a49e4, including the Package API lint, Module library tests with debug_reducers, and Wasm compilation. CI must pass before merge and tag publication. No Package source or generated artifacts changed.

Model: GPT-6.1-sol. Harness: Codex in T3 Code.

[Mathih13]

Merged as 5fe83f3. The main compatibility run passed and published api-v4 at that commit.

The collection now checks Core ca0a49e4, Package API v4. Local verification passed 37 Package API tests, 1,687 Module tests with debug_reducers, Wasm compilation, tag-publication tests, and the artifact firewall. CI also verified committed Script Artifacts. Older API tags remain unchanged.