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/test/ui.lua

@@ -18,7 +18,9 @@ fs = {
 }
 
 local savedTheme = "light"
-settings = {
+local frameWidth, frameHeight = 320, 480
+
+screen = {
   getTheme = function()
     return savedTheme
   end,
@@ -26,11 +28,6 @@ settings = {
     savedTheme = name
     return true
   end,
-}
-
-local frameWidth, frameHeight = 320, 480
-
-gui = {
   FONT_SMALL = 0,
   FONT_UI = 1,
   FONT_BODY = 2,
@@ -70,7 +67,7 @@ local function interactiveNodes()
   return result
 end
 
-node = {
+tree = {
   reset = function()
     nodes, focus, buttonCount = {}, nil, 0
   end,
@@ -204,13 +201,13 @@ ui.mount(function()
 end)
 
 assert(ui.down(10, 10))
-assert(node.isPressed(first))
+assert(tree.isPressed(first))
 assert(ui.move(95, 10))
-assert(not node.isPressed(first))
+assert(not tree.isPressed(first))
 assert(ui.move(10, 10))
-assert(node.isPressed(first))
+assert(tree.isPressed(first))
 assert(ui.up(10, 10))
-assert(not node.isPressed(first))
+assert(not tree.isPressed(first))
 
 local expectedTouch = { "enter", "exit", "enter", "exit", "click" }
 for index, name in ipairs(expectedTouch) do
@@ -223,13 +220,13 @@ end
 events = {}
 assert(ui.buttonPress("right", true))
 assert(ui.buttonPress("right", false))
-assert(node.getFocus() == first)
+assert(tree.getFocus() == first)
 assert(ui.buttonPress("right", true))
-assert(node.getFocus() == second)
+assert(tree.getFocus() == second)
 assert(ui.buttonPress("confirm", true))
-assert(node.isPressed(second))
+assert(tree.isPressed(second))
 assert(ui.buttonPress("confirm", false))
-assert(not node.isPressed(second))
+assert(not tree.isPressed(second))
 assert(ui.buttonPress("back", true) == false)
 
 local expectedButtons = {
@@ -271,7 +268,7 @@ frameWidth, frameHeight = 320, 480
 -- still is. Which node was hit is geometry, so the test names the target directly.
 ui.reset()
 local pressedCalls = {}
-node.setPressed = function(_, on)
+tree.setPressed = function(_, on)
   pressedCalls[#pressedCalls + 1] = on
 end
 local own, styled
@@ -281,7 +278,7 @@ ui.mount(function()
   return ui.box { own, styled }
 end)
 local target
-node.hit = function()
+tree.hit = function()
   return target
 end