Implement skill resolution and recent skill tracking in tools

[madebyaris]

• Added resolve_requested_commands method to SkillCatalog for resolving requested skill names, handling duplicates, and returning errors for unknown skills.
• Enhanced InvokeSkillTool and SpawnSubagentTool to utilize RecentSkillHints for tracking recently used skills and passing them to child sessions.
• Updated spawn_subagent functionality to accept a list of skills, allowing child sessions to load relevant skills automatically or inherit the most recent one.
• Added tests to ensure correct behavior for skill resolution and recent skill tracking.
• Updated documentation to reflect new features and usage of skills in subagent tasks.

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Summary by cubic

Adds skill resolution and recent-skill tracking so agents and sub-agents load the right guidance automatically. spawn_subagent now accepts explicit skills or inherits the most recent; unknown skills are validated early with helpful errors.

• New Features

  • Added SkillCatalog::resolve_requested_commands to trim, dedupe, and error on unknown skills (includes available commands in the message).
  • Introduced RecentSkillHints to track the last N loaded skills.
  • invoke_skill records successfully loaded skills into RecentSkillHints.
  • spawn_subagent accepts an optional skills array; if omitted, it inherits the most recent skill. Runtime validates skills and passes them to the child; the child’s context includes “Recommended Skills” with guidance to use invoke_skill.

• Migration

  • Constructors changed: InvokeSkillTool::new(..) and SpawnSubagentTool::new(..) now require a shared RecentSkillHints.
  • If you send SpawnRequest directly, populate the new skills: Vec<String> (use [] if none).

^{Written for commit bd6a22b. Summary will update on new commits.}

[madebyaris]

related to #46

[cubic-dev-ai]

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