feat(power): configure the active power plan from power.setup

[blendonl]

What

mshell.power.setup{ screen_off = 10, sleep = 0, power_button = "sleep", lid_battery = "hibernate" }

mshell.exe --settings get power.screen_off power.lid
mshell.exe --settings set power.sleep_battery 15

• screen_off, sleep, hibernate: minutes idle, 0 = never, 0–1440.
• power_button, sleep_button: nothing | sleep | hibernate | shutdown | display_off.
• lid: the same without display_off.
• Every field has a _battery twin for the DC value.

Why not the Settings handlers

They offer these only as translated display labels ("15 minutes (Recommended)", "Do Nothing"), so a config would break on a non-English Windows. Power rows in the catalog instead carry the power subgroup and setting GUIDs, AC or DC, and a scale; src/settings_power.c reads and writes them on the active scheme with PowerRead/WriteAC/DCValueIndex and re-applies the scheme. Everything else — Lua validation, --settings, background apply on start and reload, failure notification — is the existing settings machinery.

Values belong to the active plan, so switching plans brings that plan's own values until the next reload writes them again.

Tested

• make all with no warnings, make test, make test-asan, make meta (committed), README Lua blocks via check-config
• settings_catalog suite (2173 assertions): power rows have braced GUIDs, numeric option indices, unique setting/AC-DC pairs; engine text and read-back words for timeouts and actions
• Live on Windows 11, unelevated: all 12 fields read the same as powercfg /qh; screen_off 3 → 4 → 3 changed only the AC index (180 → 240 → 180 s); sleep_button_battery sleep → hibernate → sleep changed only the DC index; lid = display_off rejected; a 90 s plan value reads as 90 seconds and setting 3 writes 180
• Config apply in the running shell (needs this build deployed) — see "Power plan settings" in MANUAL-TESTS.md