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

skins/blizzard/help.lua

@@ -2,18 +2,6 @@ pfUI:RegisterSkin("Help", "vanilla:tbc", function ()
   local rawborder, border = GetBorderSize()
   local bpad = rawborder > 1 and border - GetPerfectPixel() or GetPerfectPixel()
 
-  -- not much here for tbc yet
-  if pfUI.client > 11200 then
-    local ticket, background = TicketStatusFrame:GetChildren()
-    CreateBackdrop(background, nil, true, .75)
-    TicketStatusFrame:SetHeight(40)
-    TicketStatusFrame:ClearAllPoints()
-    TicketStatusFrame:SetPoint("TOP", 0, -5)
-
-    UpdateMovable(TicketStatusFrame)
-    return
-  end
-
   StripTextures(HelpFrame)
   CreateBackdrop(HelpFrame, nil, nil, .75)
   CreateBackdropShadow(HelpFrame)