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/core/sys.lua

@@ -2,7 +2,7 @@
 
 -- Generated from native/src/bindings/core/sys.cpp. Do not edit.
 
----@alias Feature "touch"|"buttons"
+---@alias Feature "screen"|"touch"|"buttons"
 
 ---@class SysLib
 sys = {}
@@ -62,3 +62,13 @@ function sys.getMemory() end
 ---Whether network time synchronization has completed.
 ---@return boolean
 function sys.isClockSynced() end
+
+---Returns the active POSIX timezone rule.
+---@return string
+function sys.getTimezone() end
+
+---Applies and persists a POSIX timezone rule.
+---@param timezone string
+---@return true? ok
+---@return string? error
+function sys.setTimezone(timezone) end