v0.1.8 — spec-compliant frontmatter

Make the SKILL.md frontmatter conform to the agentskills spec: version/author moved under metadata (version a quoted string), tags/related_skills as comma-separated strings, dropped the nested metadata.hermes block. The prior frontmatter was off-spec (parsers tolerated it). Caught by a cross-environment Codex review reading the actual file against the spec — earlier summary-fed reviews never saw the frontmatter. (Unrelated to the withdrawn 0.1.8/0.1.9 timeout experiments, which were reverted; version reused.)