Migrate grounder extension to wxt + close WASM-runtime verification gap

[espetro]

Replace the hand-rolled MV3 extension (extension/manifest.json, content.js, sidepanel.js, vendored wllama/) with a wxt project mirroring play-ai/apps/extension (wxt 0.20.26, bun, vanilla TS side panel).

Why: wxt removes the hand-rolled manifest/CSP/wasm/worker risk, exposes a CDP endpoint so agent-browser can drive .output/chrome-mv3 for a real-browser smoke test (does wllama's WASM actually run under MV3 CSP?), and makes the pure grounding/DOM-extraction logic unit-testable via vitest.

Plan: .agents/plans/2026-07-16-wxt-extension.md

Scope:

• Port content.js -> entrypoints/content.ts (extract roleOf/labelOf/isVisible/extractPage for jsdom unit tests)
• Port sidepanel.js -> entrypoints/sidepanel/main.ts (npm @wllama/wllama, not vendored copy)
• Port background.js -> entrypoints/background.ts
• Port grounding.js -> lib/grounding.ts verbatim
• wxt.config.ts with CDP webExt wiring (--remote-debugging-port=9222)
• Unit tests: grounding.test.ts, content-map.test.ts
• Real-browser smoke test via agent-browser (not Playwright, per global rule)
• Delete hand-rolled files once ported

Out of scope: Firefox build target, multi-step agent behavior, model/training changes.

[espetro]

Migration done except the real-browser smoke test.

Done:

• Ported to wxt 0.20.27 (bun), mirroring play-ai/apps/extension: wxt.config.ts (manifest + CDP webExt wiring), entrypoints/background.ts, entrypoints/content.ts (+ lib/content-map.ts for the testable DOM-extraction), entrypoints/sidepanel/{index.html,main.ts}, lib/grounding.ts (verbatim prompt/parsing logic).
• Unit tests: 17/17 passing (grounding.test.ts, content-map.test.ts under vitest+jsdom).
• Typecheck clean (tsc --noEmit).
• bun run build succeeds; .output/chrome-mv3/manifest.json has the expected permissions, CSP, and wllama's wasm/worker assets are emitted (content-scripts/content.js, assets/wllama-*.wasm).
• Hand-rolled manifest.json/content.js/sidepanel.js/background.js/sidepanel.html/vendored wllama/ deleted; README refreshed.

Blocked: the real-browser CDP smoke test (agent-browser driving .output/chrome-mv3). Chrome itself launches fine with --load-extension (confirmed via process inspection — the extension loads), but agent-browser's own daemon control-socket hung indefinitely on every attempt in this environment, reproduced even with a trivial control-group extension (bare manifest, no wllama/wasm), so it's an agent-browser/environment issue, not a defect in the ported code. Left for a manual "load unpacked" check or a retry once the tooling issue is resolved.