ruby: enable and verify psych/YAML on Kandelo

[brandonpayton]

Purpose

Enable and verify Ruby psych/YAML on Kandelo (kd-egn1).

main already builds Ruby with psych/YAML wired in build-ruby.sh (libyaml 0.2.5,
--with-ext=...,psych,...), but there is no ruby.rb Homebrew formula and no
runtime test that require 'yaml' + YAML.load/dump actually work on the platform.
This PR adds the psych-including formula and a Node runtime smoke, and verifies psych
works at runtime.

Changes

• homebrew/kandelo-homebrew/Formula/ruby.rb (new): Ruby 4.0.5 formula that builds
  through the resolver (psych/YAML included) and whose test block exercises
  require 'yaml' with a YAML.dump/YAML.load round-trip in addition to the basic
  interpreter check.
• packages/registry/ruby/demo/yaml-smoke.ts (new): a Node runtime smoke that runs
  the built ruby.wasm under the kernel host (host-fs passthrough so RUBYLIB
  resolves) and asserts the YAML round-trip, printing the psych/libyaml versions.

Coordination (important)

This keeps/verifies psych, which directly conflicts with PR #810 (kd-p3hr): #810's
build-ruby.sh deletes the libyaml block and sets --with-out-ext=...,psych, i.e.
merging #810 as-is would regress psych/YAML off main. This PR relies on main's
psych-enabled build-ruby.sh and does not modify it. The #810 psych removal must be
reconciled (not merged) — flagged to the coordinator. Published-bottle acceptance
tracks kd-yuef.

Verification

• Ruby built via build.sh + build-ruby.sh: libyaml 0.2.5 built, psych compiled and
  statically linked (psych.a); runtime stdlib includes psych.rb/yaml.rb.
• Node runtime smoke (npx tsx packages/registry/ruby/demo/yaml-smoke.ts):
  PASS — psych=5.3.1 libyaml=0.2.5; require 'yaml' + YAML.dump/YAML.load
  round-trip succeed. Outcome lists: test-runs/kd-egn1/yaml-node-smoke/outcome-lists/
  (1 passed / 0 failed / 1 skipped).
• Browser smoke: skipped here — published-bottle/browser acceptance tracks kd-yuef;
  local Node runtime is verified.

Bead: kd-egn1 (initiative: homebrew-all; follow-up of kd-p3hr)

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