build: run the browser e2e suites in CI (closes #259)

Nothing automatic ran either e2e suite, so every browser-level guarantee in this
wallet -- WebAssembly under the shipped CSP, the recovery-phrase and private-key
DOM wipes, the ConfirmTx spend gate, the dApp approval round trips -- held only
when a human or an agent remembered to run it by hand.

.gitea/workflows/e2e.yml adds two jobs, e2e-chrome and e2e-firefox, one per
browser so a Chrome failure cannot hide the Firefox result. They are separate
from the check workflow: REPO_POLICIES.md caps make test at 20 seconds and
script/cibuild is a docker build whose Dockerfile runs make check, so neither the
cap nor the local fast path is touched. make check is byte-for-byte unchanged.

Neither suite could run on the runner as it stood, and the reason is not
docker-in-docker. The runner executes a job inside a container against the HOST's
docker daemon, and the job's checkout lives on a docker volume rather than a host
path, so `docker run -v "$PWD:/work"` is resolved by the host, silently succeeds
and mounts an empty directory -- measured on this runner. The runner image's node
is also too old to install this repo's dependencies. Both suites therefore ship
the repo to the daemon as a build context and build the extension inside the
pinned image, which leaves docker as the only prerequisite on a runner or a
laptop. The suites themselves are unchanged; only how the repo reaches the
container is.

Both scripts now build with --iidfile and run the image by ID rather than by tag,
so two clones running a suite at once on the same host cannot swap it under each
other.

The jobs report, they do not gate. Whether a check blocks a merge is Gitea branch
protection, which this repo does not configure, so a failure is a red mark a
reviewer must account for. Nothing can pass vacuously: no continue-on-error, no
`|| true`, and both scripts exit non-zero when docker is missing, when the image
build fails and when the browser fails to start.

README.md

@@ -83,10 +83,11 @@ provide:
   git pre-commit hook
 - `script/projectname` — print the project name (used for the Docker image tag)
 - `script/test` — run the test suite (jest)
-- `script/test-e2e` — run the Chrome browser end-to-end suite (docker required;
-  see [End-to-End Tests](#end-to-end-tests))
-- `script/test-e2e-firefox` — run the Firefox browser end-to-end suite (docker
-  required; builds its own pinned image, see
+- `script/test-e2e` — run the Chrome browser end-to-end suite (docker is the
+  only prerequisite: it builds a pinned image that carries the repo and a fresh
+  extension build, see [End-to-End Tests](#end-to-end-tests))
+- `script/test-e2e-firefox` — run the Firefox browser end-to-end suite (same,
+  against an image with a pinned Firefox and geckodriver, see
   [End-to-End Tests](#end-to-end-tests))
 - `script/lint` — run the linter
 - `script/fmt` — format all files (writes)
@@ -136,11 +137,12 @@ are outside `make check`.
 
 `make test-e2e` builds `dist/chrome/` and drives the **real popup in a real
 Chrome**, loaded as an unpacked MV3 extension inside a pinned
-`mcr.microsoft.com/playwright` container (pinned by digest in `script/test-e2e`;
-docker is required and the suite fails loudly rather than skipping if it is
-unavailable). The suite lives in `tests/e2e/` and is driven by
-`playwright-core`, whose version must stay matched to the container's Playwright
-version — the browsers ship inside the image.
+`mcr.microsoft.com/playwright` container (pinned by digest in
+`tests/e2e/Dockerfile`, which is also where the extension is built; docker is
+required and the suite fails loudly rather than skipping if it is unavailable).
+The suite lives in `tests/e2e/` and is driven by `playwright-core`, whose
+version must stay matched to the container's Playwright version — the browsers
+ship inside the image.
 
 It covers popup load, WebAssembly compilation under the shipped CSP (see
 [Content Security Policy](#content-security-policy)), wallet creation through
@@ -320,9 +322,37 @@ Two limits are worth knowing, both real differences from the Chrome suite:
 Neither `make test-e2e` nor `make test-e2e-firefox` is part of `make check` or
 `make test`. `REPO_POLICIES.md` caps `make test` at 20 seconds and a browser
 suite does not fit; nothing in `tests/e2e/` is named `*.test.js`, so jest cannot
-pick it up either. Neither is wired into the Gitea workflow yet —
-docker-in-docker in CI is a separate question. Run them locally before changing
-anything under `src/popup/views/`.
+pick it up either. Run them locally before changing anything under
+`src/popup/views/`.
+
+### In CI
+
+`.gitea/workflows/e2e.yml` runs both suites on every push, as two jobs —
+`e2e-chrome` and `e2e-firefox` — separate from the `check` workflow, so the
+20-second `make test` cap and the local fast path are untouched. Each job is a
+checkout and the matching `script/` entrypoint, nothing else.
+
+Docker is the only thing either job needs from the runner, and that is not an
+accident. The runner executes a job inside a container against the **host's**
+docker daemon, so a `docker run -v "$PWD:/work"` source path is resolved by the
+host and mounts an empty directory, and the runner image's node is too old to
+install this repo's dependencies. Both suites therefore ship the repo to the
+daemon as a build context and build the extension inside the image, which works
+identically on a laptop.
+
+The jobs **report, they do not gate.** A failure is a red mark against the
+commit that a reviewer has to account for, not a hard block: whether a check
+blocks a merge is Gitea branch protection, which this repo does not configure.
+
+Nothing in either job can pass vacuously. There is no `continue-on-error` and no
+`|| true`; both scripts exit non-zero when docker is missing, when the image
+build fails, and when the browser fails to start; the Chrome harness aborts the
+suite outright if its network interception is not in effect.
+
+Measured on this repo's runner: `e2e-chrome` about 1m55s cold, almost all of it
+the one-time pull of the pinned ~800MB Playwright layer, and well under a minute
+once that layer is cached. `e2e-firefox` about 1m05s cold, and it caches its
+Firefox and geckodriver downloads the same way.
 
 ## Rationale