refactor(api)!: one namespace per feature, screen split out

Namespaces were shared across features: `settings` was written by core, the
panel and touch, and `input` by touch and buttons. That made "does this
firmware implement the whole feature?" a question no pointer could answer.

Each namespace now belongs to exactly one feature or to core, so a feature is
a provider pointer and the compiler validates completeness:

  gui, node       -> screen, tree, under the screen feature
  settings        -> screen (rotation, theme), sys (timezone),
                     touch (calibration)
  input           -> touch, buttons

Runtime::open() no longer requires a GuiProvider; a firmware without one runs
with no screen/tree globals and reports sys.hasFeature("screen") false.
Rotation is one value again: GuiProvider::setRotation applies and persists, so
an app rotating the panel transiently puts the old value back itself.

lua/api/features/buttons.lua

@@ -5,33 +5,33 @@
 ---@alias Button "up"|"down"|"left"|"right"|"confirm"|"back"
 
 -- Roles, not physical buttons: a device maps whatever hardware it has onto them, and
--- up/down/left/right are the directions node.moveFocus already takes.
+-- up/down/left/right are the directions tree.moveFocus already takes.
 
----@class InputLib
-input = input or {}
+---@class ButtonsLib
+buttons = {}
 
 ---Returns the roles this device reports, so an app can label only the actions it has.
 ---@return Button[]
-function input.getButtons() end
+function buttons.getAll() end
 
 ---Whether any button is held.
 ---@return boolean
-function input.isAnyPressed() end
+function buttons.isAnyPressed() end
 
 ---Whether a button is held.
 ---@param button Button
 ---@return boolean
-function input.isPressed(button) end
+function buttons.isPressed(button) end
 
 ---Whether a button went down since the last poll.
 ---@param button Button
 ---@return boolean
-function input.wasPressed(button) end
+function buttons.wasPressed(button) end
 
 ---Whether a button came up since the last poll.
 ---@param button Button
 ---@return boolean
-function input.wasReleased(button) end
+function buttons.wasReleased(button) end
 
 ---Fired when a button goes down.
 ---@param button Button