kprintf: migrate all uart_print() calls to kprintf() (Route A)

kprintf: migrate all uart_print() calls to kprintf() (Route A)

Replace 270 direct uart_print() calls across 42 files with kprintf(),
routing all kernel messages through the klog ring buffer and multi-backend
console infrastructure (UART + VGA).

Key changes:
- All kernel log/debug messages now go through kprintf() -> klog_append()
  -> console_write(), ensuring they appear in dmesg and on all enabled
  output devices.
- Consolidated multi-call patterns (uart_print+itoa_hex) into single
  kprintf() calls with format specifiers (%x, %u, %s, %d, %c).
- Removed manual itoa/itoa_hex + uart_print concatenation throughout.
- Cleaned up stale #include uart_console.h from files that no longer
  need it (main.c, socket.c, syscall.c, slab.c, timer.c).
- uart_print() now only remains in 2 places:
  * uart_console.c (the implementation)
  * console.c (the UART backend in console_write)
- uart_put_char() retained in tty.c for direct terminal I/O (not logging).
- arch_early_setup files keep uart_console.h for uart_init() call.

Build: clean, cppcheck: clean, smoke: 19/19 pass.