Make the kiosk autologin survive a reboot, and allow forcing a display mode

Two problems on musicdolphin, found after its first reboot.

getty@tty1 was never enabled. The role installed the autologin drop-in and the
handler restarted the unit, which works until the next boot - these images do
not enable getty@tty1 themselves, getty.target pulls in getty-static.service and
nothing else, so after a reboot nobody logs in and the kiosk never starts. Enable
it as well as starting it.

And the attached screen reads back 0 bytes of EDID on both micro-HDMI ports while
reporting "disconnected", so the kernel offers no modes, no framebuffer is
created, and X exits with "no screens found". That is the signature of a cable or
adapter whose DDC/HPD lines are broken but whose video pairs are fine. Forcing
the connector on is not enough on its own - with no EDID there is still no mode
to set - so allow a `video=` kernel parameter, which forces the output and names
the mode. hdmi_force_hotplug=1 is no use here; vc4-kms-v3d ignores it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

roles/pi_kiosk/defaults/main.yml

@@ -1,3 +1,14 @@
 ---
 pi_kiosk_user: "kiosk"
 pi_kiosk_url: "http://localhost:8080"
+
+# Force a mode on the kiosk output, as a `video=` kernel parameter, e.g.
+# "HDMI-A-1:1920x1080@60e" (the trailing `e` forces the output enabled). Empty means
+# "let EDID decide", which is what you want whenever EDID can be read.
+#
+# This is for a display the Pi cannot see: a micro-HDMI cable or adapter whose DDC/HPD
+# lines are broken but whose video pairs are fine reads back 0 bytes of EDID and
+# reports "disconnected", while displaying perfectly once a mode is forced. Note
+# hdmi_force_hotplug=1 does nothing here - it is ignored by the vc4-kms-v3d driver
+# these images use.
+pi_kiosk_force_mode: ""