chore: initial scaffold for latprobe CLI tool

Sets up project structure, working conventions (CLAUDE.md), README with
the full assignment and roadmap, seeded CHANGELOG, and a buildable Go
scaffold (Step 0) with flag parsing and stub probe types.

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

CHANGELOG.md

@@ -0,0 +1,14 @@
+# Changelog
+
+All completed features are logged here in reverse-chronological order.
+
+---
+
+## 2026-07-01 00:08 — Project scaffold (Go, Step 0)
+
+- Created project structure: `go/`, `python/`, `docs/plans/`, `docs/usage/`
+- Initialised Go module `latprobe` (`go/go.mod`)
+- Minimal `go/main.go` that prints usage and exits cleanly when no URL is given
+- Stub `go/internal/probe/probe.go` defining the `Result` type and `Measure` signature
+- Foundation files: `README.md`, `CLAUDE.md`, `CHANGELOG.md`
+- Saved initial plan to `docs/plans/2026-07-01-00-08-go-latency-tool.md`