[Build/Test] Keep kernel smoke fixtures out of package publishing - #802

Why

The small Wasm programs used by kernel and host smoke tests are repository-built test fixtures. They are not distributable packages or Homebrew formulae.

Keeping a kernel-test-programs package manifest made package tooling treat seven unrelated fixtures as one multi-output package. The atomic package resolver would then move their paths into a package directory, even though their real producer and consumers intentionally use the flat test-fixture paths.

What changes

• Remove kernel-test-programs from the package registry and browser-package exceptions.
• Add a versioned test-artifact inventory that records each architecture-specific fixture, source, producer, resolver path, and every source consumer.
• Check that the inventory is complete, paths are safe, sources and consumers exist, and no unrecorded literal consumer appears.
• Record the old hello.wasm entry as retired; examples/hello.c remains a separate SDK example.
• Make the worker-entry test request the actual wasm64 hello64 fixture instead of relying on an incorrect wasm32 default-path fallback.
• Document shared test-artifact ownership under tests/test-artifacts.

This changes test/build ownership only. It does not change the kernel, ABI, host runtime behavior, or production deployment.

Validation

Current-main local validation:

• package-system suite: 11 files, 89 tests passed
• focused ownership/browser/fetch tests: 17 tests passed
• inventory consumer/path audit passed
• worker-entry test loaded successfully and skipped because this clean worktree had no built fixture bytes
• git diff --check

The pull request CI will provide exact-head Node, browser, POSIX, libc, Sortix, and staging evidence before merge.