Route slash registration through pfUI.api.RegisterSlashCommand

The RegisterSlashCommand helper in api/api.lua was effectively unused
(only macrotweak called it); every other command hand-rolled the
SLASH_*/SlashCmdList pair. Convert the existing manual registrations to
the helper with force=true, preserving the current always-bind behavior
while centralizing the pattern behind one code path (and its _G. and
conflict-check handling).

Left as-is: pfUI.lua's /rl, /pfui, /gm (registered before api.lua
defines the helper) and the vendored libs' debug commands.

modules/share.lua

@@ -389,9 +389,8 @@ pfUI:RegisterModule("share", function ()
       end)
     end
 
-    _G.SLASH_PFEXPORT1, _G.SLASH_PFEXPORT2, _G.SLASH_PFEXPORT3 = "/export", "/import", "/share"
-    function SlashCmdList.PFEXPORT(msg, editbox)
+    pfUI.api.RegisterSlashCommand("PFEXPORT", { "/export", "/import", "/share" }, function(msg, editbox)
       f:Show()
-    end
+    end, true)
   end
 end)