skillscript-runtime v0.19.6

v0.19.5 tag was pushed but the release pipeline failed: the new
regression test for the bundled hello-world.skill.md had a hardcoded
absolute path (/Users/scotts/Development/skillscript/...) that
worked locally but ENOENT'd in CI. No artifact shipped (no npm publish,
no GHCR push).

Fix in v0.19.6: same regression test, now using REPO_ROOT-relative
resolution (fileURLToPath(import.meta.url)-derived). All other
v0.19.5 fixes carry forward unchanged.

Lesson: CI-only path failures slip past local probes. Worth pinning a
test for the test surface itself — but the simpler discipline is "never
hardcode an absolute path in a test." Sibling to v0.19.5's own banked
lesson.