feat(render): dual-driver render layer — omp-native browser on omp, playwright on pi/CLI

[rz1989s]

What

Removes keystone's dependency on bundling/loading a browser driver on omp by splitting the render flow (engine/render-core.mjs) behind two drivers:

Driver	Path	Used by
engine/driver-playwright.mjs (lazy specifier, #21 trick unchanged)	engine/render.mjs	CLI (check-gates --render, audit) + the keystone_render pi extension tool
engine/driver-omp-native.mjs (omp's built-in Puppeteer browser via the eval-kernel browser global)	engine/render-omp.mjs	omp hosts — the skill imports it from omp's eval kernel

extensions/render.ts now skips registration on omp (engine/host.mjs: argv0/bunfs detection — env vars are unreliable, omp mirrors OMP_* to PI_*). Pi behavior is unchanged. The tsx bootstrap in check-gates.mjs/audit.mjs is gone; tsx dropped from deps.

Skill § 7.2 branches by host: keystone_render tool on pi, one-line eval-kernel import of engine/render-omp.mjs on omp. engine.md / gates.md / README updated to the render-layer framing.

Why

• omp's extension loader preloads every resolvable import specifier; a static playwright-core reference cost ~20s/startup (omp startup: static playwright-core import in render.ts makes loadExtensions take ~20s #21, lazy-avoided since 1.0.3). With the extension inert on omp, playwright-core is never loaded there at all — the whole class (loader preload, install drift à la plugin install: lock.json version drifts from installed code; doctor misses it; upgrade rejects npm-scope plugins can1357/oh-my-pi#11090) is out of scope for omp.
• omp bundles its own Chromium (Puppeteer); using it removes the second driver stack (Expose the built-in browser to extension tools (so plugins don't need to bundle puppeteer/playwright) can1357/oh-my-pi#11091 — ctx.invokeTool can't reach browser today, so the eval-kernel import is the working seam).
• Same gate engine everywhere: render-core is driver-agnostic and a behavioral port (viewports loop, hero@1280-only, OKLCH canon, clickables@1280+375, artifacts contract).

omp-native driver specifics (discovered live on omp 18.1.12)

• tab.screenshot() returns a temp-file path → copy to artifact
• tab.run serializes fns — closures don't cross; expressions bridge via { args }
• settle wait via waitForSelector("body") (playwright's networkidle isn't exposed)

Verification

• pnpm test 179 pass / 1 skip (~5s); pnpm test:render 4/4 with real Chromium; test:lint 103/103; typecheck clean; lockfile regenerated (--frozen-lockfile green)
• omp-native driver end-to-end in a live omp session: exact viewport metrics (innerWidth 1280/375, height = w×0.625), OKLCH computed pairs, hero rects at 1280 only, clickables at 1280+375, real screenshot bytes (15.1 KB / 23.3 KB)
• CLI audit.mjs path mode: full 5-viewport artifact set + report in 3.3s
• Extension skip live: repo linked as omp plugin → no keystone tool registered (NONE), zero startup warnings

Version

1.1.0 (package.json bumped here; tag v1.1.0 after merge triggers the release workflow).