Add nightly Maestro E2E workflow

docs/testing.md

@@ -29,6 +29,44 @@ adb reverse tcp:3000 tcp:3000
 - In a second tab, run `pnpm e2e:build`
 - In a third tab, run `pnpm e2e:run __e2e__`
 
+## Nightly Maestro CI
+
+The `Nightly Maestro E2E` GitHub Actions workflow runs every day at 04:00 UTC
+and can also be started from the Actions tab with **Run workflow**. It runs iOS
+and Android concurrently, but each platform runs all of `__e2e__/config.yml`
+sequentially on one explicitly selected simulator or emulator. The flows share a
+stateful mock-server manager, so the suite must not be sharded.
+
+The jobs run Maestro CLI 2.6.1 locally on GitHub Actions; Maestro Cloud is not
+used. iOS runs on `macos-26-xlarge` with Xcode 26.4. Android runs on
+`Linux-x64-32core`. Both use Java 17 and the Node and pnpm versions declared in
+`package.json`.
+
+The mock-server manager listens on host port 1986 and creates test services on
+port 3000. Metro listens on 8081. Android reverses ports 3000 and 8081 into the
+emulator; port 1986 remains host-side because Maestro JavaScript calls it from
+the runner. Android uses the existing Docker Compose PostgreSQL 14 and Redis 7
+services on ports 5433 and 6380. GitHub-hosted macOS cannot run nested Docker
+virtualization, so iOS provisions ephemeral native PostgreSQL 14.x and Redis
+7.4.7 on those same ports and starts `pnpm --dir dev-env start:external`.
+
+Each platform uploads a `nightly-e2e-<platform>-<run-id>` artifact for 14 days.
+It contains JUnit at `report.xml`, Maestro screenshots, videos, command metadata
+and `maestro.log` under `maestro/`, plus Metro, native build, mock-server, service,
+dependency, and translation logs. The workflow always uploads what was captured,
+including when setup or the native build fails before Maestro starts.
+
+Add the repository secret `E2E_FAILURES_SLACK_WEBHOOK` before enabling the
+schedule. The aggregation job runs even when either platform fails and posts one
+detailed Slack notification containing both job statuses, failed flow details or
+the failed setup phase, the commit and workflow links, and links to both artifact
+sets. Successful runs do not post to Slack.
+
+Before relying on the schedule, manually dispatch the workflow and verify both
+platforms against live Metro and `dev-env`, Android localhost routing, artifact
+uploads on success and failure, one Slack message for a forced failure, and no
+Slack message for an all-green run.
+
 ## Using Flashlight for Performance Testing
 1. Make sure Maestro is installed (optional: only for automated testing) by following the instructions above
 2. Install Flashlight by following [these instructions](https://docs.flashlight.dev/)