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/driver.h

@@ -0,0 +1,56 @@
+/**
+ * @file driver.h
+ * @brief Kernel driver architecture.
+ *
+ * Provides a simple framework for registering and initializing kernel drivers.
+ * Each driver provides a probe function that returns whether it should load,
+ * and an init function that performs the actual initialization.
+ *
+ * Drivers are registered at compile time using the REGISTER_DRIVER macro,
+ * which places driver descriptors in a special linker section. The kernel
+ * iterates over all registered drivers during boot.
+ */
+
+#ifndef DRIVER_H
+#define DRIVER_H
+
+#include <stdint.h>
+
+/** Driver probe result codes. */
+typedef enum {
+    DRIVER_PROBE_OK = 0,        /**< Driver should be loaded. */
+    DRIVER_PROBE_NOT_FOUND = 1, /**< Hardware not found, skip this driver. */
+    DRIVER_PROBE_ERROR = 2      /**< Error during probing. */
+} driver_probe_result_t;
+
+/**
+ * Driver descriptor structure.
+ *
+ * Each driver provides a name, a probe function (to test if hardware is
+ * present), and an init function (to set up the driver).
+ */
+typedef struct driver {
+    const char *name;                     /**< Human-readable driver name. */
+    driver_probe_result_t (*probe)(void); /**< Probe function. Returns DRIVER_PROBE_OK if driver should load. */
+    int (*init)(void);                    /**< Init function. Returns 0 on success, non-zero on failure. */
+} driver_t;
+
+/**
+ * Register a driver.
+ *
+ * Places the driver descriptor in the .drivers linker section so it
+ * is automatically discovered during boot.
+ */
+#define REGISTER_DRIVER(drv) \
+    static const driver_t * __attribute__((used, section(".drivers"))) \
+    _driver_##drv = &(drv)
+
+/**
+ * Initialize all registered drivers.
+ *
+ * Iterates over the .drivers section, probes each driver, and initializes
+ * those that respond positively to probing.
+ */
+void init_drivers(void);
+
+#endif /* DRIVER_H */