fix: remove duplicate docstrings from public functions in .c files

Public function docstrings belong exclusively in .h headers per
coding convention. Only static helper functions and static variables
retain docstrings in .c files. Removed 413 duplicate docstrings
across 185 files (15 CBM + 15 C SDK projects). All 30 projects
rebuild with zero errors.

drivers/0x01_uart/0x01_uart.c

@@ -49,14 +49,6 @@
 /** @brief UART baud rate in bits per second */
 #define UART_BAUD    115200
 
-/**
- * @brief Application entry point for the UART uppercase echo demo
- *
- * Initializes UART0 and enters an infinite loop that reads incoming
- * characters, converts them to uppercase, and echoes them back.
- *
- * @return int Does not return
- */
 int main(void) {
     uart_driver_init(UART_TX_PIN, UART_RX_PIN, UART_BAUD);
     uart_driver_puts("UART driver ready (115200 8N1)\r\n");

drivers/0x01_uart/uart.c

@@ -35,63 +35,30 @@
 /** @brief Hardware UART instance used by this driver */
 #define UART_INST uart0
 
-/**
- * @brief Initialize hardware UART0 on the specified TX and RX GPIO pins
- *
- * @param tx_pin   GPIO pin number to use as UART0 TX
- * @param rx_pin   GPIO pin number to use as UART0 RX
- * @param baud_rate Desired baud rate in bits per second
- */
 void uart_driver_init(uint32_t tx_pin, uint32_t rx_pin, uint32_t baud_rate) {
     uart_init(UART_INST, baud_rate);
     gpio_set_function(tx_pin, GPIO_FUNC_UART);
     gpio_set_function(rx_pin, GPIO_FUNC_UART);
 }
 
-/**
- * @brief Check whether a received character is waiting in the UART FIFO
- *
- * @return bool true if at least one byte is available to read
- */
 bool uart_driver_is_readable(void) {
     return uart_is_readable(UART_INST);
 }
 
-/**
- * @brief Read one character from UART0 (blocking)
- *
- * @return char The received character
- */
 char uart_driver_getchar(void) {
     return (char)uart_getc(UART_INST);
 }
 
-/**
- * @brief Transmit one character over UART0 (blocking)
- *
- * @param c Character to transmit
- */
 void uart_driver_putchar(char c) {
     uart_putc_raw(UART_INST, c);
 }
 
-/**
- * @brief Transmit a null-terminated string over UART0
- *
- * @param str Pointer to the string to transmit
- */
 void uart_driver_puts(const char *str) {
     while (*str) {
         uart_putc_raw(UART_INST, *str++);
     }
 }
 
-/**
- * @brief Convert a character to uppercase
- *
- * @param c Character to convert
- * @return char Uppercase version if 'a'-'z', otherwise unchanged
- */
 char uart_driver_to_upper(char c) {
     if (c >= 'a' && c <= 'z') {
         return (char)(c - 32);