fix(battery): prefer Mains/USB supplies when auto-detecting the adapter

[klizas]

What does this PR do?

Fixes battery adapter auto-detection picking the battery itself as the adapter.

When no "adapter" is configured, refreshBatteries() assigns adapter_ to the last node in /sys/class/power_supply that has online or status. Batteries match through status, so whether the real adapter or the battery wins depends on readdir order. A battery has no online, so when the battery wins, every adapter_ check reads offline: the Not charging -> Plugged upgrade and full-at-plugged are silently dead.

Observed on a MacBookPro16,1 (kernel 7.2.0-1-cachyos-t2): ADP1 (ACPI0003:00, type Mains, has online, no status) iterates before BAT0 (ACPI0002:00, type Battery, has status, no online), so BAT0 always won and the bar showed the discharging/not-charging format while plugged in. Pinning "adapter": "ADP1" was the only workaround.

The fix classifies candidates by type and picks in priority order:

1. node matching a configured "adapter" name (unchanged behavior)
2. Mains
3. USB* (prefix match, so legacy pre-4.19 types like USB_PD count)
4. any other online-capable supply (Wireless, UPS, missing type file)
5. status-only nodes, as a last resort

First match wins within each tier. If a pass finds nothing, adapter_ keeps its previous value, as before.

Tested live on the machine above: before, Waybar picked BAT0, patched now picks ADP1, and Plugged works without a pin. Also compared old and new selection over nine mocked sysfs layouts (battery-only, Mains+battery, Mains+USB-C source nodes, legacy USB_PD, wireless charger, UPS-only, typeless online node, empty dir, two batteries): the new logic finds an adapter in every case the old one did, and picks the same node everywhere except the order-dependent broken cases. Battery-only machines still get the battery as adapter_, and the configured-name path is identical.

Related issues

None found

Checklist

• Code is formatted with clang-format
• Builds locally (ninja -C build)
• Man page updated for any new/changed user-facing option (man/) — N/A, no new option; adapter docs already say "instead of auto detect"
• Tested against the affected module(s)