Tests against a fake Frame, and a headset smoke test

tests/fakeframe: a container that stands in for the Frame (Arch Linux, or
Arch Linux ARM on arm64) with sshd, rsync, Valve's steamos-devkit-service
and hooks (vendored unmodified), a fake Steam client for the devkit pipe and
the DevTools port (the app's JavaScript runs in Node against stand-in
SteamClient/appStore objects), stubs for steam, wpctl, flatpak, podman,
Lepton and friends, battery and thermal files under /sys, and fault
switches (fakeframe-ctl): pairing mode, approve/deny/timeout, Steam not
running, headset asleep, sshd off, disk full, runtimes missing. A second
container is the computer running Frame Control.

tests/e2e: 29 tests driving the real ui/server.py, frame_connect.py and
frame_titles.py against it; skipped unless FRAME_E2E=1. scripts/e2e.sh
builds, runs and tears down; CI runs it on ubuntu-24.04-arm.

tests/smoke + scripts/frame-smoke.sh: the core cases against a real Frame,
recorded with its BUILD_ID, cleaning up after itself; --pair to pair a
throwaway key. docs/testing.md describes the layers.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/fakeframe/rootfs/usr/lib/os-release

@@ -0,0 +1,9 @@
+NAME="SteamOS"
+PRETTY_NAME="SteamOS"
+ID=steamos
+ID_LIKE=arch
+LOGO=steamos
+HOME_URL="https://www.steampowered.com/"
+VERSION_ID=0.3.0
+VARIANT_ID=vr
+BUILD_ID=20260922.6101926