Add Event Gateway agent plugin and evals - #307

Thanks for this — reviewed as part of the v2.5.0 triage. Holding it out of that release (which is bug fixes only), but it's close and there's no conflict blocking it: plugins/ doesn't exist on main, so all six new files land cleanly. mergeStateStatus: BEHIND just means the branch needs updating.

Two things worth resolving first.

1. The Skill won't be loaded in this repo at that path.

AGENTS.md:586 sets the convention:

Location: Repo-specific agent skills live under skills/ at the repository root

and .claude/skills, .cursor/skills and .agents/skills are all symlinks to ../skills. A skill at plugins/hookdeck-event-gateway/skills/hookdeck-event-gateway/SKILL.md sits outside that tree, so neither Claude Code nor Cursor will pick it up when working in this repo.

That may well be intentional — the plugin is a distributable package, not a repo-local skill, and those are different things. If so, could you add a line to AGENTS.md § Agent skills distinguishing the two locations? Otherwise the next person adding a skill has two contradictory examples. (Related: I've just deduplicated .agents/skills into a symlink in #336, since it had drifted into a byte-identical copy.)

2. It sits under a stale "read-only" sentence.

The hunk lands inside ### Event Gateway MCP, whose opening line (README.md:577) still describes the server as exposing "read-only tools". That was already inaccurate — hookdeck_connections does pause/unpause, and the README's own tool table says so — but this PR makes the mismatch louder, since the Skill's whole premise is approval-gated mutating actions. Worth fixing that sentence in the same PR.

Verified as accurate: the anchor line still exists on main (now at README.md:607), so the hunk will offset cleanly; the relative link resolves once merged; both plugin.json files and cases.jsonl parse; and every command the SKILL.md references exists — hookdeck gateway mcp (pkg/cmd/mcp.go:18), and connection/source/destination/transformation/event/request/attempt/metrics/issue all resolve under gateway. The capability list maps onto the documented tools with nothing invented.

One question: telvine (in the plugin README's packaging section) and the skill.invoked / skill.completed / skill.error telemetry vocabulary don't appear anywhere else in this repo — the CLI's own telemetry is in pkg/cmd/telemetry.go and uses different events. Are those aspirational, or is there tooling behind them we should link to?