Define recommended _meta keys for skill resources

[olaservo]

Background

PR #53 (skill URI scheme proposal) mentions that servers MAY use the _meta field for additional skill metadata, but doesn't yet specify what keys would be useful based on existing needs and implementations.

Multiple implementations likely already use or could benefit from structured metadata on skill resources — e.g., version, tags, dependencies, authorship. Defining a recommended set of _meta keys would improve interoperability between servers and clients without requiring protocol changes.

Scope

1. Survey what metadata skill implementations currently expose or need (e.g., NimbleBrain annotations, Agent Skills spec frontmatter)
2. Propose a recommended set of _meta keys for skill resources with descriptions and example values
3. Consider alignment with Agent Skills spec frontmatter fields, including common examples of custom metadata being added in frontmatter

Acceptance Criteria

• Survey of metadata patterns across at least 3 existing implementations
• Proposed set of recommended _meta keys with types and descriptions
• At least 2 example resources/list responses showing _meta usage
• Cross-reference from the skill URI scheme doc (once PR Define well-known URI schemes and naming patterns for skill resources #53 merges)

References

• PR #53: Skill URI Scheme Proposal (mentions _meta without specifying keys)
• Agent Skills spec frontmatter
• MCP Resources specification