fix(rovodev): preserve skill compatibility frontmatter on round-trip

[dyoshikawa]

Summary

Partially addresses #1986. Fixes the skills sub-gap: RovodevSkillFrontmatterSchema declared name/description/allowed-tools/license/metadata but not compatibility, and toRulesyncSkill/fromRulesyncSkill map fields explicitly, so the documented optional Agent Skills compatibility field was silently dropped on round-trip (a residual of #1696).

Changes

• Add compatibility (free-form string; object form accepted for back-compat) to RovodevSkillFrontmatterSchema and to the rulesync skill rovodev section schema/type.
• Carry compatibility through both round-trip mappings, mirroring the agentsskills/vibe adapters.
• Extend the round-trip test and the file-formats docs.

Deferred: event-hooks adapter

The issue's primary gap — a RovodevHooks adapter writing the eventHooks block into ~/.rovodev/config.yml — is intentionally not implemented here. The exact eventHooks YAML schema is not officially documented: it is a preview feature surfaced only via the interactive /hooks command, and both primary sources (the Atlassian blog and the settings docs) describe the interactive flow without publishing the literal key/nesting structure. The issue itself flags this: "Confirm the schema against a live /hooks help / config dump before implementing." Implementing it now would mean inventing a schema that could emit config Rovo Dev cannot read, so it remains blocked on schema confirmation. This PR uses Refs (not Closes) so #1986 stays open for the hooks work.

Test

pnpm cicheck (code + content) passes.

Refs #1986