feat: add PHONY declarations and docs target to Makefile (#9)

---
name: "Default Template"
about: "The default template for `lambda`."
title: "feat: add PHONY declarations and docs target to Makefile"
ref: "main"
assignees: []
labels: []
---

## Description

This PR improves the Makefile by adding proper `.PHONY` declarations and a new `docs` target.
The `.PHONY` declarations ensure make properly handles targets that don't create files.
The `docs` target provides an easy way to view Go package documentation locally using godoc.

Changes:
- Add `.PHONY` declaration for all non-file targets (`it`, `run`, `profile`, `explain`, `graph`, `docs`).
- Add `docs` target that runs godoc server on port 6060 with helpful usage message.

### Decisions

None.

## Benefits

- Prevents make from getting confused if files with target names exist.
- Provides convenient documentation viewing with `make docs`.
- Improves Makefile maintainability following best practices.

## Checklist

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

Reviewed-on: #9
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

Makefile

@@ -1,5 +1,7 @@
 BINARY_NAME=lambda.exe
 
+.PHONY: it run profile explain graph docs
+
 it:
 	@ go build -o ${BINARY_NAME} ./cmd/lambda
 	@ chmod +x ${BINARY_NAME}
@@ -19,3 +21,7 @@ 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
+
+docs:
+	@ echo ">>> View at 'http://localhost:6060/pkg/git.maximhutz.com/max/lambda/'"
+	@ go run golang.org/x/tools/cmd/godoc@latest -http=:6060