Move druid mana bar into the unit frame, off nampower

The druid secondary mana bar (shown while shapeshifted into a form that
uses energy/rage) lived in nampower.lua and read base mana through
nampower's GetUnitField. Extract it into the unit frame proper and drive
it with ClassicAPI instead:

- Create pfDruidMana_<unit> as f.druidmana in CreateUnitFrame (player and
  target), lay it out in UpdateConfig from the existing C.unitframes.druidmana*
  keys, and update it in a new pfUI.uf:UpdateDruidMana driven by the frame's
  own base-refresh pass (UNIT_MANA / UNIT_DISPLAYPOWER). No separate event
  frames, no nampower dependency.
- Read mana via UnitPower(unit, 0) / UnitPowerMax(unit, 0), the ClassicAPI
  slot getters that return the mana pool regardless of the active power, so
  it works while in Cat/Bear form.
- Add a "Show Druid Mana Bar Text" toggle (druidmanatext) so the current/max
  readout can be hidden while keeping the bar; config default, GUI checkbox,
  and locale stubs.
- Remove the now-dead block from nampower.lua.

api/config.lua

@@ -231,6 +231,7 @@ function pfUI:LoadConfig()
   pfUI:UpdateConfig("unitframes", nil,           "druidmanaoffy",    "0")
   pfUI:UpdateConfig("unitframes", nil,           "druidmanaspace",   "-3")
   pfUI:UpdateConfig("unitframes", nil,           "druidmanatexture", "Interface\\AddOns\\pfUI\\img\\bar")
+  pfUI:UpdateConfig("unitframes", nil,           "druidmanatext",    "1")
 
   pfUI:UpdateConfig("unitframes", nil,           "combowidth",       "6")
   pfUI:UpdateConfig("unitframes", nil,           "comboheight",      "6")