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

libs/libunitscan.lua

@@ -165,34 +165,30 @@ libunitscan:SetScript("OnEvent", function()
   end
 end)
 
--- since TargetByName can only be triggered within vanilla,
--- we can't auto-scan targets on further expansions.
-if pfUI.client <= 11200 then
-  -- setup sound function switches
-  local SoundOn = PlaySound
-  local SoundOff = function() return end
+-- setup sound function switches
+local SoundOn = PlaySound
+local SoundOff = function() return end
 
-  libunitscan:SetScript("OnUpdate", function()
-    -- don't scan when another unit is in target
-    if UnitExists("target") or UnitName("target") then return end
+libunitscan:SetScript("OnUpdate", function()
+  -- don't scan when another unit is in target
+  if UnitExists("target") or UnitName("target") then return end
 
-    local name = next(queue)
-    if name then
-      -- disable sound
-      _G.PlaySound = SoundOff
+  local name = next(queue)
+  if name then
+    -- disable sound
+    _G.PlaySound = SoundOff
 
-      -- try to target the unknown unit
-      TargetByName(name, true)
-      ClearTarget()
+    -- try to target the unknown unit
+    TargetByName(name, true)
+    ClearTarget()
 
-      -- enable sound again
-      _G.PlaySound = SoundOn
+    -- enable sound again
+    _G.PlaySound = SoundOn
 
-      queue[name] = nil
-    end
+    queue[name] = nil
+  end
 
-    this:Hide()
-  end)
-end
+  this:Hide()
+end)
 
 pfUI.api.libunitscan = libunitscan