ci: add missing pack:mcpb/validate:mcpb scripts

[asachs01]

Summary

• Part of the MCPB broken-partial cleanup (boss-assigned, task_1790730039511_66382409, from forge's 2026-09-30 fleet census -- see WYRE-AI/ops-runbooks#6 for the measured numbers/method).
• manifest.json has been present and complete since repo creation (manifest_version 0.3, real server.entry_point/mcp_config/user_config), but the corresponding packaging scripts were never added -- a genuine finish, not vestigial cruft to remove.
• Copies the reference scripts/pack-mcpb.js (halopsa-mcp's fixed version, already scoped-name-safe per ops-runbooks#5) verbatim and wires pack:mcpb/validate:mcpb into package.json.
• Verified end-to-end locally: npm run pack:mcpb builds and produces a correctly-named bundle at repo root.

Test plan

• npm run pack:mcpb — produces a valid bundle locally
• Human review / merge

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[coderabbitai]

Important

Draft PR not reviewed

Draft PRs are not automatically reviewed by default.

• Trigger a manual review

To automatically review draft PRs, update your CodeRabbit configuration:

reviews:
  auto_review:
    drafts: true

---

_{Comment @coderabbitai help to get the list of available commands.}