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

modules/castbar.lua

@@ -306,8 +306,8 @@ pfUI:RegisterModule("castbar", "vanilla", function ()
         end
 
       elseif event == CASTBAR_EVENT_CAST_START or event == CASTBAR_EVENT_CHANNEL_START then
-        playerarg = pfUI.client <= 11200 or arg1 == "player" and true or nil
-        if playerarg then this.delay = 0 end
+        playerarg = true
+        this.delay = 0
       end
     end)
 
@@ -391,9 +391,7 @@ pfUI:RegisterModule("castbar", "vanilla", function ()
     pfUI.castbar.focus.spacing = default_border * 2 + tonumber(C.unitframes.focus.pspace) * GetPerfectPixel()
 
     -- reset unitstr for vanilla focus frame emulation
-    if pfUI.client <= 11200 then
-      pfUI.castbar.focus.unitstr = nil
-    end
+    pfUI.castbar.focus.unitstr = nil
 
     local anchor = pfUI.uf.focus.portrait:GetHeight() > pfUI.uf.focus:GetHeight() and pfUI.uf.focus.power or pfUI.uf.focus
     local width = C.castbar.focus.width ~= "-1" and C.castbar.focus.width or anchor:GetWidth()