Implement VGA text-mode driver with memory statistics display (AI)

- Created VGA driver that writes to the 0xB8000 text-mode framebuffer.
  Supports 80x25 display with 16 foreground/background colors, scrolling,
  hardware cursor updates, and special characters (\n, \r, \t, \b).
- Provides vga_puts, vga_putchar, vga_put_hex, vga_put_dec, vga_set_color.
- Displays boot banner ("ClaudeOS v0.1 booting...") on screen clear.
- vga_show_mem_stats() prints total RAM, kernel start/end addresses, and
  kernel size on the VGA display during boot.
- Registered as the first driver using REGISTER_DRIVER, proving the
  driver framework works end-to-end (probe -> init lifecycle).

Tested: driver loads successfully, debug port confirms vga probe/init.

README.md

@@ -48,7 +48,7 @@ Once a task is completed, it should be checked off.
 - [x] Create a paging subsystem. It should allow drivers to allocate and deallocate pages at will.
 - [x] Create a memory allocator. This should provide the kernel with `malloc` and `free`. Internally, it should use the paging subsystem to ensure that the address it returns have actual RAM paged to them.
 - [x] Create an initial driver architecture, allowing different drivers included in the kernel to test whether they should load or not.
-- [ ] Create a VGA driver. On startup, some memory statistics should be displayed, as well as boot progress.
+- [x] Create a VGA driver. On startup, some memory statistics should be displayed, as well as boot progress.
 - [ ] Create subsystem for loading new processes in Ring 3.
 - [ ] Update the build script to generate a ramdisk containing any applications to run. This initial ramdisk is in CPIO format.
 - [ ] Write a VFS subsystem.