phase 2 removing tbc

Strip dead pfUI.client > 11200 and pfUI.expansion == "tbc" branches now
that vanilla is the only supported client.

- pfUI.lua: hardcode expansion = "vanilla"; collapse force_region matrix
- compat/vanilla.lua, libs/{libcast,libdebuff,libtotem,libunitscan,
  focus}: drop always-false early-returns
- api/unitframes.lua: delete TargetBuffOnUpdate poller + tbc visibility
  and secure-template branches; click-cast keeps only vanilla path
- api/ui-widgets.lua: unconditional EffectiveScale divide
- env/tables.lua: drop unused focus/focustarget pfValidUnits entries
- modules/actionbar.lua: simplify EnablePaging, drop ButtonSwitch/
  petvisibility, unwrap prowl block, single keybind-remap path
- modules/{castbar,chat,cooldown,loot,questitem,totems}: unwrap
  always-true conditionals
- modules/nameplates.lua: cfg-only fake-cooldown gate, unwrap overlap/
  clickthrough + mouselook blocks
- modules/friends.lua + skins/blizzard/friends.lua: maxtab = 4
- skins/blizzard/{help,game_menu,questlog}: drop tbc-only branches

api/ui-widgets.lua

@@ -34,7 +34,7 @@ do -- statusbars
 
       if self.mode == "vertical" then
         height = self:GetHeight()
-        if pfUI.expansion == "vanilla" then height = height / self:GetEffectiveScale() end
+        height = height / self:GetEffectiveScale()
         point = height / (self.max - self.min) * (val - self.min)
 
         -- keep values in limits
@@ -53,7 +53,7 @@ do -- statusbars
         self.bg:SetPoint("BOTTOMRIGHT", self, "BOTTOMRIGHT", 0, point)
       else
         width = self:GetWidth()
-        if pfUI.expansion == "vanilla" then width = width / self:GetEffectiveScale() end
+        width = width / self:GetEffectiveScale()
         point = width / (self.max - self.min) * (val - self.min)
 
         -- keep values in limits