Stop disabled buttons taking the hover border colour

S:HandleButton ends with an unconditional OnEnter/OnLeave pair that swaps
the border to the value colour and back, and neither handler looks at
IsEnabled. A disabled button still fires both scripts on this client, so
the greyed Activate button, Save changes with nothing pending and Purchase
with nothing selected all lit up under the cursor and read as clickable.

HookScript can't be undone, but handlers fire in registration order, so a
hook registered after HandleButton runs last and has the final say on the
colour. Skin:Button wraps HandleButton with that hook, and every call site
in the plugin now goes through it, so the correction is inherited rather
than repeated per module.

The Activate button carries the border from its own update as well:
activating a spec disables it under the very cursor that just clicked it,
and OnEnter has been and gone by then, so nothing else would put the border
back until the pointer moved off.

Skin:IsEnabled hoists the 0/1-to-boolean normalisation this client needs
out of UpdateActivateState, which held the only copy of it.

Modules/Skinning.lua

@@ -138,6 +138,74 @@ function Skin:HideArt(frame)
 	frame:Hide()
 end
 
+-- Buttons ---------------------------------------------------------------------
+--
+-- IsEnabled hands back 0 and 1 on this client rather than false and true
+-- (probed), and 0 is truthy in Lua, so every enabled check has to normalise
+-- what it gets back before comparing it.
+function Skin:IsEnabled(button)
+	local state = button.IsEnabled and button:IsEnabled()
+
+	return state ~= nil and state ~= false and state ~= 0
+end
+
+-- The target is resolved the way ElvUI's own SetModifiedBackdrop and
+-- SetOriginalBackdrop resolve it -- the backdrop when the button has one, the
+-- button itself otherwise -- or the colour lands on something that isn't the
+-- object drawing the border.
+local function SetButtonBorder(button, lit)
+	local backdrop = button.backdrop or button
+	if not backdrop.SetBackdropBorderColor then return end
+
+	backdrop:SetBackdropBorderColor(unpack(lit and E.media.rgbvaluecolor or E.media.bordercolor))
+end
+
+-- S:HandleButton ends with an unconditional pair of OnEnter/OnLeave hooks that
+-- swap the border to the value colour and back, and neither of them looks at
+-- IsEnabled. A disabled button still fires both scripts on this client, so a
+-- dead button lights up under the cursor and reads as clickable -- the greyed
+-- Activate button, Save changes with nothing pending, Purchase with nothing
+-- selected. HookScript can't be undone, but handlers fire in registration
+-- order, so a hook registered after HandleButton runs last and has the final
+-- say on the colour.
+--
+-- This one deliberately doesn't consult IsMouseOver: OnEnter can fire a pixel
+-- before IsMouseOver turns true (ElvUI's own aura code pads around the same
+-- quirk), and reading it here would drop the highlight off a live button.
+local function OnButtonEnter(button)
+	if Skin:IsEnabled(button) then return end
+
+	SetButtonBorder(button, false)
+end
+
+-- For a button that can be disabled while the cursor is already on it: OnEnter
+-- has been and gone by then, so nothing corrects the border until the pointer
+-- leaves. Only worth wiring up where something already watches the button's
+-- state -- it does not justify an OnUpdate of its own.
+function Skin:RefreshButtonBorder(button)
+	SetButtonBorder(button, self:IsEnabled(button) and button:IsMouseOver())
+end
+
+-- Every S:HandleButton call site in the plugin goes through here, so the
+-- disabled-hover correction is inherited rather than repeated per module. The
+-- extra arguments are HandleButton's own (strip, isDeclineButton,
+-- useCreateBackdrop, noSetTemplate) and are passed straight through.
+function Skin:Button(button, ...)
+	if not button then return end
+
+	S:HandleButton(button, ...)
+
+	-- Guarded separately from HandleButton's own isSkinned flag: these frames
+	-- re-run their skin pass on every show, and HookScript stacks handlers
+	-- rather than replacing them, so an unguarded re-hook adds another copy
+	-- per show for the life of the session.
+	if not button.CoAButtonSkinned then
+		button.CoAButtonSkinned = true
+
+		button:HookScript("OnEnter", OnButtonEnter)
+	end
+end
+
 -- Several of these controls draw their art as anonymous regions of one atlas
 -- file rather than through the named Left/Middle/Right fields or the Normal/
 -- Pushed/Disabled set S:HandleButton knows how to clear, so its own clearing
@@ -205,7 +273,7 @@ function Skin:Dropdown(dropdown, menu)
 	dropdown.CoASkinned = true
 
 	self:StripArtByFile(dropdown, DROPDOWN_ART)
-	S:HandleButton(dropdown)
+	self:Button(dropdown)
 	SkinDropdownCaret(dropdown)
 
 	self:Panel(menu)