test: containerized Chrome end-to-end harness that drives the real popup (closes #181)

`make check` was green while the AddToken screen crashed on every open.
`script/lint` is only `prettier --check`, so a used-but-not-imported
identifier is invisible until a browser evaluates it. This adds a suite
that runs the real popup in a real Chrome and treats any uncaught page
error or console.error as a failure.

- `script/test-e2e` (with `make test-e2e` as a thin shim) builds
  `dist/chrome/` and runs `tests/e2e/run.js` inside the Playwright image,
  pinned by digest. `playwright-core` is pinned to the matching 1.56.0
  through `yarn.lock`; the two must be bumped together because the
  browsers ship inside the image.
- Deliberately outside `script/test` and `script/check`: REPO_POLICIES
  caps `make test` at 20 seconds. Nothing under `tests/e2e/` is named
  `*.test.js`, so jest cannot pick it up either.
- Launches with `channel: "chromium"`; the default headless shell
  silently refuses to load extensions with no error at all. The extension
  id is read from the service worker URL, never hardcoded.
- All http(s) traffic is intercepted at the browser level and served from
  fixtures, so the run is deterministic and offline. Unrecognised
  outbound requests are reported as failures rather than allowed.
- A missing build or an unavailable container fails loudly; a skip that
  looks like a pass is the failure mode this is meant to prevent.
- One allowlisted page error, for the libsodium WASM CSP fallback tracked
  as #182, which is otherwise untouched here.

The suite was demonstrated failing against the unfixed tree with
`pageerror: showView is not defined` and `pageerror: addressDotHtml is
not defined`, so it carries the two one-line import fixes it caught:

closes #150 — `showView` restored to the destructure in
`src/popup/views/addToken.js`, dropped by a22f33d, which made the
AddToken screen unreachable and corrupted the navigation stack.

closes #151 — `addressDotHtml` restored in
`src/popup/views/transactionDetail.js`, dropped by df031fd, which threw
before `showView("transaction")` for every ERC-20 transfer. The shared
`renderAddressHtml` helper is not used here on purpose: it hardcodes the
`/address/` explorer URL, and this row needs the token-specific `/token/`
link.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: bootstrap setup install test lint fmt fmt-check check docker hooks build clean dev
+.PHONY: bootstrap setup install test test-e2e lint fmt fmt-check check docker hooks build clean dev
 
 # Standard targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -16,6 +16,10 @@ install:
 test:
 	@script/test
 
+# Browser end-to-end suite. Requires docker; not part of check.
+test-e2e:
+	@script/test-e2e
+
 lint:
 	@script/lint