Implement file system API and add shutdown functionality for desktop builds

core/include/nova64_fs.h

@@ -0,0 +1,39 @@
+#ifndef NOVA64_FS_H
+#define NOVA64_FS_H
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stddef.h>
+
+/* ========================================================================== */
+/* File System API                                                            */
+/* ========================================================================== */
+
+/**
+ * @brief Reads a file from the filesystem into a buffer.
+ *        Supports drive identifiers: "SYS:" (internal system store),
+ *        "EXA:" (cartridge slot 0), "EXB:" (cartridge slot 1), etc.
+ * @param file_path Null-terminated file path with drive identifier
+ *                  (e.g., "SYS:/init.wasm" or "EXA:/game.wasm").
+ * @param buffer Pointer to destination buffer where file contents will be
+ *               copied.
+ * @param buffer_size Size in bytes of the destination buffer.
+ * @return True if file was successfully read into buffer, false on error
+ *         (file not found, read error, or buffer too small).
+ * @note Uses the sd_read_sector callback from nova64_io_interface_t.
+ *       The callback must be registered via nova64_init() before calling
+ *       this function.
+ */
+bool nova64_read_file_to_buffer(const char *file_path, uint8_t *buffer,
+                                size_t buffer_size);
+
+/**
+ * @brief Gets the size of a file in the filesystem.
+ * @param file_path Null-terminated file path with drive identifier
+ *                  (e.g., "SYS:/init.wasm" or "EXA:/game.wasm").
+ * @return Size of the file in bytes on success, or -1 on error
+ *         (file not found, read error, etc.).
+ */
+int32_t nova64_get_file_size(const char *file_path);
+
+#endif // NOVA64_FS_H