chore(metrics): weekly launch-metrics snapshot

[alimaandev]

Adds a weekly metrics tracker for the 0.7.0 launch:

• \scripts/metrics.mjs\ (\pnpm run metrics): snapshots GitHub stats via \gh\ (stars, forks, contributors, open issues) + npm weekly downloads + action repo popularity, appends/updates a dated row in METRICS.md (idempotent per day, --json\ mode for raw output)
• \METRICS.md: baseline row — stars 1, forks 1, contributors 2, open issues 3, weekly downloads 254, action stars 0
• \eslint.config.mjs: allow \etch\ global for scripts; package.json: \metrics\ script

Tracking targets: 1K stars, 10K weekly downloads, 100 action installs, 5 contributors, PH top-5, HN front page.