Add Maelstrom to resource bar color options

[Rubyj]

What does this change?

Adds Maelstrom to the list of configurable resource bar colors in the Resource Bar settings page (Bars > Resource Bar > Resource Colors).

Why?

Shamans use the Maelstrom resource type, which was not included in the POWER_LIST used to generate color pickers. Users who set all listed resource colors (e.g. to black) would still see Shaman resource bars rendered in Blizzard's default blue, because there was no override entry for the MAELSTROM token.

Changes

• Options/Options.lua — Added { token = "MAELSTROM", name = L["Maelstrom"] } to POWER_LIST
• Locales/enUS.lua — Added L["Maelstrom"] = true (alphabetically sorted)

No new settings keys, no migration needed, no logic changes. Follows the identical pattern used by all other power types. The existing GetPowerColor, profile export/import, and Reset All to Default button all handle Maelstrom automatically once it's in the list.

[Rubyj]

@DanderBot anything else needed here?