Add initial project structure and implement async main for Pico W

Makefile

@@ -1,26 +1,39 @@
 DIRENV := $(shell command -v direnv 2> /dev/null)
+
+# If we have direnv and we're not already in the environment, re-exec via direnv
 ifdef DIRENV
-    EXEC := direnv exec .
+    ifeq ($(origin DIRENV_DIR), undefined)
+        # Ensure direnv is allowed
+        _ALLOW := $(shell direnv allow . > /dev/null 2>&1)
+        # Re-exec make via direnv
+        EXEC := direnv exec . $(MAKE)
+build run test clean flatpak-build:
+	@$(EXEC) $@
+    else
+        # We are already inside direnv, or direnv is not available
+        EXEC :=
+    endif
 else
     EXEC :=
 endif
 
+ifndef EXEC
 build:
-	$(EXEC) cargo build
+	cargo build
 
 run:
-	$(EXEC) cargo run
+	cargo run
 
 test:
-	$(EXEC) cargo test
+	cargo test
 
 clean:
-	$(EXEC) cargo clean
+	cargo clean
-
-.PHONY: build run test clean
-
 
 # Flatpak build target
 .PHONY: flatpak-build
 flatpak-build:
-	$(EXEC) flatpak-builder --force-clean build-flatpak flatpak/app.flatpak.json
+	flatpak-builder --force-clean build-flatpak flatpak/app.flatpak.json
+endif
+
+.PHONY: build run test clean