Use ClassicAPI animation groups for fades and pulses

Replace hand-rolled OnUpdate alpha loops with engine animation groups:
unit frame aggro/combat glow, tracking icon pulse, new-mail blink,
castbar fade-out, autohide, XP/rep bar fade, info box timeout and the
unlock-mode scale label. Timing no longer depends on framerate, and the
always-running glow driver and tracking OnUpdate are gone.

The XP bar tracks hover through OnEnter/OnLeave instead of MouseIsOver,
so a fade can't restart under the cursor.

modules/castbar.lua

@@ -36,7 +36,7 @@ pfUI:RegisterModule("castbar", function ()
       cb.bar:SetValue(1)
     end
     if cb.bar.spark then cb.bar.spark:Hide() end
-    cb.fadeout = 1
+    if cb:GetAlpha() > 0 and not cb.fade:IsPlaying() then cb.fade:Play() end
   end
 
   -- "Spellname (N)" label for an active tradeskill merge — N is the number
@@ -94,8 +94,8 @@ pfUI:RegisterModule("castbar", function ()
     cb.activeName = name
     cb.isTradeskill = isTradeskill
     cb.delay = (delayMs or 0) / 1000
+    cb.fade:Stop()
     cb:SetAlpha(1)
-    cb.fadeout = nil
 
     -- Shield an uninterruptible cast. Not on the player's own bar: the flag is
     -- measured against the reader's own interrupts and silences, so on your own
@@ -248,8 +248,14 @@ pfUI:RegisterModule("castbar", function ()
     cb.bar.spark:SetPoint("BOTTOM", cb.bar, "BOTTOMLEFT", 0, 0)
     cb.bar.spark:Hide()
 
-    -- OnUpdate animates the bar fill and fades it out on completion. All
-    -- state transitions (cast start/stop/interrupt, channel start/stop,
+    -- Fade-out after a cast ends. The bar stays at alpha 0 while idle.
+    cb.fade = cb:CreateAnimationGroup()
+    local fade = cb.fade:CreateAnimation("Alpha")
+    fade:SetChange(-1)
+    fade:SetDuration(.4)
+    cb.fade:SetScript("OnFinished", function() cb:SetAlpha(0) end)
+
+    -- OnUpdate animates the bar fill. All state transitions (cast start/stop/interrupt, channel start/stop,
     -- pushback) come from the event handler below — we never poll C_Spell
     -- here.
     cb:SetScript("OnUpdate", function()
@@ -257,15 +263,12 @@ pfUI:RegisterModule("castbar", function ()
       this.tick = GetTime() + 0.020 -- ~50 FPS
 
       if this.drag and this.drag:IsShown() then
+        this.fade:Stop()
         this:SetAlpha(1)
         return
       end
 
-      if this.fadeout and this:GetAlpha() > 0 then
-        this:SetAlpha(this:GetAlpha() - 0.05)
-        if this:GetAlpha() <= 0 then this.fadeout = nil end
-        return
-      end
+      if this.fade:IsPlaying() then return end
 
       if not this.endTime then
         if this:GetAlpha() ~= 0 then this:SetAlpha(0) end