nameplates: cachedGuid + percent-mode guard + name text position

- Switch the four GUID reads in OnDataChanged from plate.parent:GetName(1)
  (SuperWoW idiom) to plate.cachedGuid (set by NAME_PLATE_UNIT_ADDED via
  UnitGUID(token)). Move the initial OnDataChanged call out of
  OnConfigChange's CREATE path so it runs after UNIT_ADDED has populated
  cachedGuid; re-add it explicitly in the user-config-change loop.

- Reject GetUnitField's health/maxHealth when maxHealth == 100 — the
  engine writes (hp_percent, 100) into UnitFields for non-detailed units
  (UPDATE_PARTIAL packets carry percent only). Without this guard,
  Nampower's raw field read returns the percent and the nameplate displays
  "5 / 100" as if it were real HP. Mirrors libhealth's heuristic so we
  fall through to its estimator instead.

- New config: nametextpos (LEFT/CENTER/RIGHT, defaults to CENTER).
  Decouple the bar's anchor from the name so the name's JustifyH can
  shift left/right without dragging the bar with it.

api/config.lua

@@ -866,6 +866,7 @@ function pfUI:LoadConfig()
 
   pfUI:UpdateConfig("nameplates", nil,           "showhp",           "0")
   pfUI:UpdateConfig("nameplates", nil,           "hptextpos",        "RIGHT")
+  pfUI:UpdateConfig("nameplates", nil,           "nametextpos",      "CENTER")
   pfUI:UpdateConfig("nameplates", nil,           "hptextformat",     "curmaxs")
   pfUI:UpdateConfig("nameplates", nil,           "vpos",             "-10")
   pfUI:UpdateConfig("nameplates", nil,           "width",            "120")