chore: add root Makefile with namespaced targets

Namespaced go-* targets (build, run, test, test-verbose, check, cover,
fmt, vet, tidy, install, lint, clean) plus umbrella targets that delegate
to them. help is the default. py-* targets will slot in during the Python
port. Updates .gitignore with coverage artifacts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -105,6 +105,26 @@ connection timings via custom socket wrap or `httpx`/`urllib3` hooks).
 
 ---
 
+## Development
+
+A `Makefile` at the repo root provides all common tasks:
+
+```sh
+make              # list all targets
+make build        # build go/latprobe
+make test         # run all tests
+make check        # fmt + vet + test (pre-commit gate)
+make go-run ARGS="https://example.com"
+make go-test-verbose
+make go-cover     # coverage report → go/coverage.html
+make go-lint      # golangci-lint
+make clean        # remove build artifacts
+```
+
+See [`docs/usage/makefile.md`](docs/usage/makefile.md) for the full target reference.
+
+---
+
 ## Development Environment
 
 - Go 1.26.4 / darwin arm64