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.

native/src/bindings/features/buttons.cpp

@@ -32,18 +32,18 @@ int wasReleased(lua_State* state) {
   return 1;
 }
 
-// @lua-augment input InputLib
+// @lua-module buttons ButtonsLib
 // @lua-preamble ---@alias Button "up"|"down"|"left"|"right"|"confirm"|"back"
 // @lua-preamble
 // @lua-preamble -- Roles, not physical buttons: a device maps whatever hardware
 // it has onto them, and
-// @lua-preamble -- up/down/left/right are the directions node.moveFocus already
+// @lua-preamble -- up/down/left/right are the directions tree.moveFocus already
 // takes.
-const luaL_Reg INPUT_FUNCTIONS[] = {
+const luaL_Reg FUNCTIONS[] = {
     // ---Returns the roles this device reports, so an app can label only the
     // actions it has.
     // @return Button[]
-    {"getButtons", getButtons},
+    {"getAll", getButtons},
     // ---Whether any button is held.
     // @return boolean
     {"isAnyPressed", isAnyPressed},
@@ -65,7 +65,8 @@ const luaL_Reg INPUT_FUNCTIONS[] = {
 } // namespace
 
 void registerButtons(lua_State* state) {
-  augmentGlobal(state, "input", INPUT_FUNCTIONS);
+  luaL_newlib(state, FUNCTIONS);
+  lua_setglobal(state, "buttons");
 }
 
 } // namespace bindings