Add PR-description skill, org-standards review agent, and pre-push check

[aalavala]

Tooling built while working NWP-101, split onto its own branch since it's not part of that ticket:

• .claude/skills/northwind-pr/: writes PR descriptions in the team's exact required shape (title, what changed, how it was verified, acceptance criteria, deliberately not done) — /submit already deferred to a skill by this name if one exists.
• .claude/agents/org-standards.md: read-only subagent (Read/Grep/Glob only) that audits a diff against every numbered item in docs/ORG-STANDARDS.md, citing item number, file, and line per finding.
• .claude/hooks/pre-push-check.sh + its registration in .claude/settings.json: a PreToolUse Bash hook that runs npm test and npm run build in build-battle/merchant-console before any git push, blocking with the failing command and its log path if either fails.

Ticket

Closes NWP-____

What changed

How I verified it

• npm test passes
• New behavior is covered by a test
• Checked it in the browser

Acceptance criteria

Bugs fixed along the way

Notes for the reviewer