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>

go/go.mod

@@ -0,0 +1,3 @@
+module latprobe
+
+go 1.26.4

go/internal/probe/probe.go

@@ -0,0 +1,34 @@
+// Package probe measures per-phase HTTP request latency.
+package probe
+
+import "time"
+
+// Phase holds the measured duration of a single request phase.
+// A zero Duration means the phase did not occur (e.g. TLS on plain HTTP).
+type Phase struct {
+	Duration time.Duration
+	// Present is false when the phase was skipped (e.g. no TLS for http://).
+	Present bool
+}
+
+// Result holds all timing phases for a single HTTP request.
+type Result struct {
+	URL      string
+	DNS      Phase
+	Connect  Phase
+	TLS      Phase
+	TTFB     Phase // server processing: WroteRequest → GotFirstResponseByte
+	Transfer Phase // body read: GotFirstResponseByte → body closed
+	Total    Phase
+
+	// StatusCode is the HTTP response status code (0 on error).
+	StatusCode int
+	// Err is non-nil if the request failed.
+	Err error
+}
+
+// Measure performs an HTTP GET request to url and returns a populated Result.
+// It is a placeholder until Step 1 wires in the actual implementation.
+func Measure(url string) Result {
+	return Result{URL: url}
+}

go/main.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+const usageText = `latprobe — measure per-phase HTTP request latency
+
+Usage:
+  latprobe [flags] <url> [url ...]
+
+Flags:
+  -n, --count int   Number of requests per URL (default 1)
+      --json        Output results as JSON instead of text
+  -h, --help        Show this help
+
+Examples:
+  latprobe https://example.com
+  latprobe -n 5 https://example.com https://www.google.com
+  latprobe --json https://example.com | jq .
+`
+
+func main() {
+	count := flag.Int("count", 1, "number of requests per URL")
+	flag.IntVar(count, "n", 1, "number of requests per URL (shorthand)")
+	jsonOut := flag.Bool("json", false, "output results as JSON")
+
+	flag.Usage = func() { fmt.Fprint(os.Stderr, usageText) }
+	flag.Parse()
+
+	urls := flag.Args()
+	if len(urls) == 0 {
+		fmt.Fprint(os.Stderr, usageText)
+		os.Exit(1)
+	}
+
+	// Placeholders — implementations wired in per step.
+	_, _ = count, jsonOut
+
+	fmt.Fprintf(os.Stderr, "latprobe: not yet implemented (scaffold only)\n")
+	os.Exit(1)
+}