refactor: improve Makefile structure and usability (#11)

## Description

This PR refactors the Makefile to improve usability, maintainability, and cross-platform compatibility.
The changes modernize the Makefile structure and make it more user-friendly.

Changes made:
- Renamed the `it` target to `build` for better clarity and conventional naming.
- Added a `help` target as the default goal to display available targets and their descriptions.
- Moved the TEST variable to the top with other configuration variables for better organization.
- Updated binary name from `lambda.exe` to `lambda` and used `${BINARY_NAME}` variable consistently throughout.
- Replaced all `@` prefixes with the `.SILENT:` directive for cleaner syntax.
- Added a `clean` target to remove all build artifacts (binary, program.out, profile directory).
- Made the `graph` target cross-platform by replacing macOS-specific `open` command with file:// URL echo.
- Updated .gitignore to include the `lambda` binary.

### Decisions

- Used `.SILENT:` directive instead of individual `@` prefixes for a cleaner, more maintainable Makefile.
- Made `help` the default target so users can run `make` without arguments to see available commands.
- Removed platform-specific commands (like `open`) in favor of cross-platform alternatives.

## Benefits

- Improved discoverability: Users can run `make` to see all available targets.
- Better maintainability: Using `${BINARY_NAME}` variable consistently makes future changes easier.
- Cross-platform compatibility: Removed macOS-specific commands.
- Cleaner syntax: `.SILENT:` directive eliminates repetitive `@` prefixes.
- More conventional: Renamed `it` to `build` follows standard Makefile conventions.

## Checklist

- [x] Code follows conventional commit format.
- [x] Branch follows naming convention (\`<type>/<description>\`). Always use underscores.
- [x] Tests pass (if applicable).
- [x] Documentation updated (if applicable).

Reviewed-on: #11
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

.gitignore

@@ -3,6 +3,7 @@
 # https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
 #
 # Binaries for programs and plugins
+lambda
 *.exe
 *.exe~
 *.dll

Makefile

@@ -1,27 +1,43 @@
-BINARY_NAME=lambda.exe
-
-.PHONY: it run profile explain graph docs
-
-it:
-	@ go build -o ${BINARY_NAME} ./cmd/lambda
-	@ chmod +x ${BINARY_NAME}
-
+BINARY_NAME=lambda
 TEST=simple
 
-run: it
-	@ ./lambda.exe - < ./samples/$(TEST).txt > program.out
+.PHONY: help build run profile explain graph docs clean
+.DEFAULT_GOAL := help
+.SILENT:
 
-profile: it
-	@ ./lambda.exe -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+help:
+	echo "Available targets:"
+	echo "  build    - Build the lambda executable"
+	echo "  run      - Build and run the lambda interpreter (use TEST=<name> to specify sample)"
+	echo "  profile  - Build and run with CPU profiling enabled"
+	echo "  explain  - Build and run with explanation mode and profiling"
+	echo "  graph    - Generate and open CPU profile visualization"
+	echo "  docs     - Start local godoc server on port 6060"
+	echo "  clean    - Remove all build artifacts"
 
-explain: it
-	@ ./lambda.exe -x -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+build:
+	go build -o ${BINARY_NAME} ./cmd/lambda
+	chmod +x ${BINARY_NAME}
+
+run: build
+	./${BINARY_NAME} - < ./samples/$(TEST).txt > program.out
+
+profile: build
+	./${BINARY_NAME} -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+
+explain: build
+	./${BINARY_NAME} -x -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
 
 graph:
-	@ go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof
-	@ go tool pprof -svg profile/cpu.prof > profile/cpu.svg
-	@ open profile/cpu.svg
+	go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof
+	go tool pprof -svg profile/cpu.prof > profile/cpu.svg
+	echo ">>> View at 'file://$(PWD)/profile/cpu.svg'"
 
 docs:
-	@ echo ">>> View at 'http://localhost:6060/pkg/git.maximhutz.com/max/lambda/'"
-	@ go run golang.org/x/tools/cmd/godoc@latest -http=:6060
+	echo ">>> View at 'http://localhost:6060/pkg/git.maximhutz.com/max/lambda/'"
+	go run golang.org/x/tools/cmd/godoc@latest -http=:6060
+
+clean:
+	rm -f ${BINARY_NAME}
+	rm -f program.out
+	rm -rf profile/