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/etc/ssh/sshd_config

@@ -0,0 +1,21 @@
+# The fake Frame's sshd. With Developer Mode on, the Frame takes key logins and
+# the Developer Mode password for `steamos` (docs/ssh.md); the fake's password
+# is "frame". MaxSessions leaves room for Frame Control's shared connection.
+Port 22
+HostKey /etc/ssh/ssh_host_ed25519_key
+HostKey /etc/ssh/ssh_host_rsa_key
+HostKey /etc/ssh/ssh_host_ecdsa_key
+PermitRootLogin no
+PubkeyAuthentication yes
+AuthorizedKeysFile .ssh/authorized_keys
+PasswordAuthentication yes
+KbdInteractiveAuthentication no
+UsePAM no
+PrintMotd no
+MaxSessions 64
+MaxStartups 64:30:128
+# OpenSSH 9.8+ penalises an address after failed logins by refusing it for a
+# while. The pairing tests fail logins on purpose, so the fake turns that off.
+# (Whether the Frame's sshd penalises is unchecked.)
+PerSourcePenalties no
+Subsystem sftp /usr/lib/ssh/sftp-server