Add initial project structure and implement async main for Pico W

Makefile

@@ -1,14 +1,21 @@
+DIRENV := $(shell command -v direnv 2> /dev/null)
+ifdef DIRENV
+    EXEC := direnv exec .
+else
+    EXEC :=
+endif
+
 build:
-	cargo build
+	$(EXEC) cargo build
 
 run:
-	cargo run
+	$(EXEC) cargo run
 
 test:
-	cargo test
+	$(EXEC) cargo test
 
 clean:
-	cargo clean
+	$(EXEC) cargo clean
 
 .PHONY: build run test clean
 
@@ -16,4 +23,4 @@ clean:
 # Flatpak build target
 .PHONY: flatpak-build
 flatpak-build:
-	flatpak-builder --force-clean build-flatpak flatpak/app.flatpak.json
+	$(EXEC) flatpak-builder --force-clean build-flatpak flatpak/app.flatpak.json