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/lib/hints.lua

@@ -8,8 +8,8 @@ local ORDER = { "back", "left", "up", "down", "right", "confirm" }
 
 local function available()
   local roles = {}
-  if input and input.getButtons then
-    for _, role in ipairs(input.getButtons()) do
+  if buttons and buttons.getAll then
+    for _, role in ipairs(buttons.getAll()) do
       roles[role] = true
     end
   end
@@ -21,11 +21,11 @@ end
 ---@param options table|nil `y`, `font`, `color`, and `background` overrides.
 function hints.draw(actions, options)
   options = options or {}
-  local font = options.font or gui.FONT_SMALL
-  local color = options.color or gui.color(0, 0, 0)
-  local background = options.background or gui.color(255, 255, 255)
-  local height = gui.getFontHeight(font) + 6
-  local y = options.y or (gui.getHeight() - height)
+  local font = options.font or screen.FONT_SMALL
+  local color = options.color or screen.color(0, 0, 0)
+  local background = options.background or screen.color(255, 255, 255)
+  local height = screen.getFontHeight(font) + 6
+  local y = options.y or (screen.getHeight() - height)
 
   local roles = available()
   local labels = {}
@@ -35,15 +35,15 @@ function hints.draw(actions, options)
     end
   end
 
-  gui.fillRect(0, y, gui.getWidth(), height, background)
+  screen.fillRect(0, y, screen.getWidth(), height, background)
   if #labels == 0 then
     return height
   end
 
-  local slot = gui.getWidth() // #labels
+  local slot = screen.getWidth() // #labels
   for index, label in ipairs(labels) do
-    local left = slot * (index - 1) + (slot - gui.getTextWidth(font, label)) // 2
-    gui.drawText(font, left, y + 3, label, color, gui.STYLE_NORMAL, background)
+    local left = slot * (index - 1) + (slot - screen.getTextWidth(font, label)) // 2
+    screen.drawText(font, left, y + 3, label, color, screen.STYLE_NORMAL, background)
   end
   return height
 end