feat(types): execInPage, onRequest & party APIs + supports() capability helper

[Timeraa]

What

Adds the activity-facing types and tooling for three new Presence/iFrame capabilities, plus a runtime feature-detection helper so activities can adopt them safely today.

• execInPage — run a function (or a declarative, CSP-immune get/call spec) in the page's own context and await a returned value.
• onRequest — read data out of page network requests via a URL/method filter (read-only, no modification).
• party on PresenceData — show a party size on Playing activities (e.g. "2 of 5"); partyId optional, only honored on ActivityType.Playing.
• supports(target, feature) — bundled into the activity, returns true when the running extension exposes the capability. Lets activities feature-detect instead of crashing on older installs.
• ESLint rule — errors on unguarded execInPage/onRequest usage, with an autofix that wraps the call in a supports() check.

Versioning

These APIs ship with the extension in 2.14.0. They can be used as of right now: because supports() is compiled into the activity bundle, it detects the capability at runtime, so an activity guarded with supports() works on 2.14.0+ and degrades gracefully (no-op) on older extensions instead of throwing. The lint rule enforces that guard.

if (supports(presence, 'onRequest')) {
  presence.onRequest({ url: '/api/now-playing', method: 'GET' }, (req) => { /* ... */ })
}

[Bas950]

can these be Dot-paths too?

[Timeraa]

Good call — done. pick/omit now accept dot-paths (not just top-level keys), matching get/call.

Runtime change in PreMiD/Extension#780: resolvePickOmit routes keys through dot-prop, so e.g. pick: ['track.name'] narrows a call result to { track: { name } } — which previously had no CSP-immune form (get can't invoke, top-level pick keeps the whole track). The filter runs on the serialized clone, so dot-path omit can't mutate page objects. Types + docs updated here in cac217e.