feat(go): step 1 — total wall-clock latency per URL

probe.Measure performs an HTTP GET and records total elapsed time from
request start to body fully read. main.go prints URL, status code, and
total for each positional URL argument, exiting 1 on any failure.

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

CHANGELOG.md

@@ -4,6 +4,15 @@ All completed features are logged here in reverse-chronological order.
 
 ---
 
+## 2026-07-01 00:08 — Simple total latency (Go, Step 1)
+
+- `probe.Measure` performs an HTTP GET and records wall-clock total time
+- `main.go` prints URL, HTTP status code, and total duration for each URL
+- Exits with code 1 if any URL fails
+- Multiple URLs accepted as positional arguments
+
+---
+
 ## 2026-07-01 00:08 — Project scaffold (Go, Step 0)
 
 - Created project structure: `go/`, `python/`, `docs/plans/`, `docs/usage/`