Mino chapter-15

Added

• Chapter 15 custom subagents: Markdown definitions in the project's
  .agents/agents/<name>.md with YAML name (equal to the file name), description
  (at most 1,024 characters), and an optional tools list of 1 to 64 tool names that
  narrows the subagent's tools and never adds one (spawn_agent and memory_save
  cannot be listed); the body is the role text. Files are at most 64 KiB, front matter
  16 KiB, and the catalog 32 KiB; unusable definitions are skipped and named in one
  notice. Other front-matter keys, such as a model or permission mode, are ignored.
• The definitions' metadata is saved once per session in a session_agents record,
  kept by restart, /resume, /clear, and compaction, and scanned again by /new;
  older sessions get one on first use. The catalog is added to the parent's
  instructions; the role text never is.
• spawn_agent tasks are now {agent, task} objects: agent names a definition, or is
  null for a general subagent. An unknown name is rejected before confirmation. A
  role's subagent receives the definition's current body with its task as labelled
  project guidance and only the listed tools that are available; missing ones are
  reported in its result, and a definition removed since the session started fails
  only its own task. Recorded 0.14.0 calls with string tasks still replay.
• Built-in skills: Mino now embeds a create-subagent skill that guides the model in
  writing a definition with the user. It appears in every skill catalog marked
  builtin; a project skill of the same name replaces it, with a notice.
• Eval replay case subagent-role.

Changed

• Session history now writes version 5 records and reads versions 1 to 5. Releases
  up to 0.14.0 cannot read sessions written by this version, and an existing session
  gets a version 5 session_agents record as soon as this version opens or resumes
  it. A session whose skill catalog was saved by an earlier release has no
  create-subagent skill until /new.
• skill_view results start with a header: for a project skill, its directory, the
  Bash working directory, and the rule that a skill's relative paths are relative to
  its directory; for a built-in skill, a note that it has no directory. A file too
  large to return with this header fails instead.
• The default SOUL.md describes built-in skills, the skill directory rule, and
  project subagents; existing ~/.mino/SOUL.md files are not changed.