Feature Request: dynamic on/off, user-only, and name-only toggles for subagents in the TUI (parity with skills)

Skills can be turned on or off, scoped to user-only, or set to name-only invocation, all from the running session, without editing a file. Subagents have no equivalent. The only lever today is permissions.deny in a settings.json file, which needs an edit and (for project/local scope) a restart or reload to take effect.

This looks like the same gap called out in #77435 (agents have no disable-model-invocation frontmatter, so plugin agent descriptions always load) and #83547 (the agent roster is not user-controllable at all, even indirectly). Those are about what loads into context. This one is about the missing runtime control surface: even if an agent could be marked name-only or user-scoped, there is no TUI command to flip that live, the way skill management works today.

Proposed: a subagent-facing counterpart to whatever command manages skills on the fly, supporting the same three toggles: enabled/disabled, user-only scope, and name-only invocation, applied immediately without a settings.json edit or restart.