Implement driver architecture with linker-section registration (AI)

- Created driver framework with probe/init lifecycle. Drivers register via
  REGISTER_DRIVER macro which places pointers in a .drivers linker section.
- During boot, init_drivers() iterates the section, probes each driver
  (checking if hardware is present), and initializes those that respond OK.
- Added .drivers section to linker.ld with __drivers_start/__drivers_end
  symbols for iteration.
- Also added .rodata.* pattern to the .rodata section for string literals
  placed in sub-sections by the compiler.
- No drivers are registered yet; the VGA driver will be the first.

Tested: boots cleanly with driver scan completing (0 registered, 0 loaded).

src/kernel.c

@@ -8,6 +8,7 @@
 #include "pmm.h"
 #include "paging.h"
 #include "kmalloc.h"
+#include "driver.h"
 
 void offset_print(const char *str)
 {
@@ -67,6 +68,9 @@ void kernel_main(uint32_t magic, uint32_t addr) {
     init_kmalloc();
     offset_print("Memory allocator initialized\n");
 
+    init_drivers();
+    offset_print("Drivers initialized\n");
+
     /* Test kmalloc/kfree */
     uint32_t *test_alloc = (uint32_t *)kmalloc(64);
     if (test_alloc) {