feat: add project save/load with .wheel files and auto-save thread

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

fs.h

@@ -0,0 +1,21 @@
+#ifndef FS_H
+#define FS_H
+
+#include "dispatcher.h"
+
+// Initialize the auto-save thread
+void fs_init(AppState *state);
+
+// Cleanup the auto-save thread
+void fs_cleanup(void);
+
+// Trigger an auto-save (thread-safe, non-blocking)
+void fs_trigger_autosave(void);
+
+// Save project to .wheel file (called from dispatcher thread)
+int fs_save_project(const char *filename, AppState *state);
+
+// Load project from .wheel file (called from dispatcher thread)
+int fs_load_project(const char *filename, AppState *state);
+
+#endif // FS_H