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.

modules/gui.lua

@@ -2143,6 +2143,7 @@ pfUI:RegisterModule("gui", function ()
 
       CreateConfig(nil, T["Druid Settings"], nil, nil, "header")
       CreateConfig(nil, T["Show Druid Mana Bar"], C.unitframes, "druidmanabar", "checkbox", nil, nil, nil, nil)
+      CreateConfig(nil, T["Show Druid Mana Bar Text"], C.unitframes, "druidmanatext", "checkbox", nil, nil, nil, nil)
       CreateConfig(nil, T["Druid Mana Bar Height"], C.unitframes, "druidmanaheight", nil, nil, nil, nil, nil)
       CreateConfig(nil, T["Druid Mana Bar Width (-1 = auto)"], C.unitframes, "druidmanawidth", nil, nil, nil, nil, nil)
       CreateConfig(nil, T["Druid Mana Bar X-Offset"], C.unitframes, "druidmanaoffx", nil, nil, nil, nil, nil)