Migrate Complete Uninstall, composed from each addon's own uninstall helper; bump to v2.12.0

New menus/complete_uninstall.sh (Core Settings), the last of the
"destructive trio". Rather than re-implementing every addon's teardown
a second time (the legacy shape), it composes the *_do_uninstall
helpers each addon already has - if an addon's removal logic changes,
Complete Uninstall picks it up automatically.

Every addon menu with an uninstall action (CUPS, VNC, WireGuard,
Tailscale, Netbird, LMS, Squeezelite, Asterisk Intercom) plus
power_schedule's "remove all schedules" and Emergency Hotspot's disable
action were each split into a confirm-and-call wrapper (unchanged from
the user's perspective) and a silent do-the-removal helper that both
the wrapper and Complete Uninstall call.

Bug fix found while composing these: several *_do_uninstall helpers
(CUPS's apt autoremove/apt clean, VNC/WireGuard/Tailscale/Netbird's apt
remove) had a bare, unguarded apt call as their second-to-last
statement. Previously this only risked aborting that one menu action if
the package was already gone. Composed together as sequential calls
inside Complete Uninstall, the same failure would have silently
truncated the entire uninstall sequence partway through. Guarded all of
them with `|| true`.

Non-addon teardown (kiosk user/files, Node.js, LightDM/Openbox,
remaining systemd units/scripts, polkit rules, re-enabling virtual
consoles, final package cleanup) stays inline in
menus/complete_uninstall.sh, since no single addon owns those paths.

Upgrade and Full Reinstall stay in ubuntu-based-kiosk.sh only - both
are coupled to its own heredoc self-extraction of main.js/preload.js/
etc, which has no modular equivalent yet.

Full command-level stubbed test suite exercising the full 12-step
teardown, confirmation-text validation, and reboot prompt. Full
19-suite regression + real end-to-end menu navigation via install.sh
all pass.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VfsFSoRqfbRG7XAg5RoE7e

menus/power_schedule.sh

@@ -628,7 +628,12 @@ action_disable_electron_reload() {
 action_remove_all_schedules() {
     echo
     ask_yes_no "Remove ALL power/display/quiet/reload schedules?" "n" || { echo "Cancelled"; return; }
+    power_schedule_do_remove_all
+}
 
+# The actual removal, no prompt - shared with Complete Uninstall so that
+# operation doesn't need to re-implement schedule teardown a second time.
+power_schedule_do_remove_all() {
     for timer in kiosk-shutdown kiosk-display-off kiosk-display-on kiosk-quiet-start kiosk-quiet-end kiosk-electron-reload; do
         sudo systemctl stop "${timer}.timer" 2>/dev/null || true
         sudo systemctl disable "${timer}.timer" 2>/dev/null || true