[BUG] skillOverrides silently ignored for plugin-provided skills

Environment: Claude Code 2.1.220, native install, macOS 26 (Darwin 25.6.0)

Description:
skillOverrides entries for plugin-shipped skills have no effect. Setting e.g. "vercel:ai-gateway": "off" in ~/.claude/settings.json (or via the /skills UI, which happily writes the entry) leaves the skill fully listed and invocable in every session. The same overrides work correctly for skills loaded from ~/.claude/skills.

Repro:

1. Enable a skill-heavy plugin (e.g. vercel@claude-plugins-official, 28 skills).
2. In /skills, set any of its skills to "off" — or add "skillOverrides": {"vercel:ai-gateway": "off"} to user settings.
3. Start a new session: the skill still appears in the available-skills listing and can be invoked.

Expected: the override suppresses the skill like it does for personal/project skills.
Actual: silently ignored — the settings write "succeeds", so it looks like it worked.

Likely cause: the skill status resolver in the 2.1.220 bundle returns early for plugin skills before consulting overrides: if(e.type!=="prompt"||e.source==="plugin")return"on" — the skillOverrides lookup that follows is only reachable for non-plugin skills.

Impact: with large plugins there's no way to trim the skill listing short of disabling the whole plugin (losing its commands/hooks). In my setup the vercel plugin alone contributes ~28 listing entries, pushing the listing well past the point where entries get truncated.

Related: #47747 asked for granular per-plugin-skill disable as a feature (closed not-planned). This differs: the settings schema and /skills UI already accept these overrides — they just don't do anything.