feat(kernel): add PL011 UART console and arch I/O helpers

- Add IOSerial: PL011 (0x0900_0000) TX with FIFO-full polling, yield while waiting
- Add Arch/IO.h (32-bit MMIO with DSB) and Arch/CPU.h (yield, WFI)
- Extend types.h (e.g. ASCII, Address, Int/UInt aliases)
- Wire KernelMain to IOSerialPutString for early boot output
- Drop .sourcekit-lsp config; note IO glob in CMake (commented)

Kernel/Include/IO/IOSerial.h

@@ -0,0 +1,9 @@
+#pragma once
+#include <types.h>
+
+enum {
+    kUARTBaseAddress = 0x09000000, // TODO: make it dynamic by parsing DTB
+};
+
+Int32 IOSerialPutCharacter(ASCII character);
+Int32 IOSerialPutString(const ASCII* string);