Classic API Focus (#2)

* focus: migrate to FocusUnit / "focus" token / PLAYER_FOCUS_CHANGED

ClassicAPI now polyfills modern WoW's focus system: FocusUnit / ClearFocus
+ "focus" / "focustarget" unit tokens accepted by every UnitX function +
PLAYER_FOCUS_CHANGED event. Drop pfUI's GUID-juggling pseudo-frame.

- env/tables.lua: add "focus" and "focustarget" to pfValidUnits — the
  focus frames now follow the standard event-driven CreateUnitFrame path
  with f.label = "focus"
- modules/focus.lua: rewrite. Slash commands use FocusUnit / ClearFocus
  directly; no more manual frame.label/unitname/id manipulation. /focus
  <name> still does a target-swap to resolve names → units, then
  FocusUnit("target") captures the GUID before the target is restored.
  PLAYER_FOCUS_CHANGED triggers immediate frame refresh on assign/clear.
- api/unitframes.lua: delete the pseudo-focus block (per-tick "scan all
  units for matching name" loop) and the "focus"/"focustarget" special-
  case in the visibility branch — "focus" is now a real token.
- modules/castbar.lua: bind the focus castbar to unitstr = "focus" once;
  drop the OnUpdate that synced pfUI.castbar.focus from
  pfUI.uf.focus.label/unitname. UnitGUID("focus") resolves at read time.
- Drop C_Minimap.SetFocusByGUID / SetFocusByName / ClearFocus calls —
  C_Minimap subscribes to PLAYER_FOCUS_CHANGED on its own.

Net -183 lines. Focus stops being a pfUI-special pseudo-frame and
becomes "just another unit token" — same treatment as target/player.

* add nameplate to valid units

---------

Co-authored-by: Brues <5278969+brues-code@users.noreply.github.com>

api/unitframes.lua

@@ -356,7 +356,7 @@ function pfUI.uf:UpdateVisibility()
   end
 
   -- vanilla visibility
-  if self.unitname and self.unitname ~= "focus" and self.unitname ~= "focustarget" then
+  if self.unitname then
     self:Show()
   elseif visibility == "hide" then
     self:Hide()
@@ -1462,52 +1462,7 @@ function pfUI.uf.OnUpdate()
     end
   end
 
-  -- handle pseudo focus frames
-  if this.unitname and this == pfFocus then
-    local unitname = ( this.label and UnitName(this.label) ) or ""
-
-    if pfFocusTarget then -- update focus target
-      pfFocusTarget.label = this.label and this.label .. "target" or nil
-      local focustargetname = pfFocusTarget.label and UnitName(pfFocusTarget.label) or nil
-
-      if pfFocusTarget.lastUnit ~= focustargetname then
-        pfFocusTarget.lastUnit = focustargetname
-        pfFocusTarget.instantRefresh = true
-        pfUI.uf:RefreshUnit(pfFocusTarget, "all")
-      end
-    end
-
-    -- break here on unset focus frames
-    if not this.unitname or this.unitname == "focus" then return end
-
-    -- focus unit detection
-    if this.unitname ~= strlower(unitname) then
-      -- invalid focus frame
-      for unit, bool in pairs(pfValidUnits) do
-        local scan = UnitName(unit) or ""
-        if this.unitname == strlower(scan) then
-          this.label = unit
-          if this.portrait then this.portrait.model.lastUnit = nil end
-          this.instantRefresh = true
-          pfUI.uf:RefreshUnit(this, "all")
-          return
-        end
-        this.label = nil
-        this.instantRefresh = true
-        this.hp.bar:SetStatusBarColor(.2,.2,.2)
-      end
-    end
-  end
-
-  -- handle pseudo focus target visibility
-  if this.unitname and this == pfFocusTarget then
-    if pfFocus and not pfFocus.label or pfFocus.label == "" then
-      this.label = nil
-      return
-    end
-  end
-
-  if not this.label then return end
+  if not this.label or this.label == "" then return end
 
   -- update portrait on first visible frame
   if this.portrait and this.portrait.model and this.portrait.model.update then