feat(runneth-apps): add Runneth default package

[ioanahayman]

Summary

• Adds the runneth-default package as the Runneth Apps side of Phase One.
• Installs the migrated analyzing, briefing, and creative-generation skills into agent userland without changing their wording.
• Adds package instruction context for the core creative skills list that is moving out of the protected Runneth volume.
• Registers the package in package-index.json with updatePolicy: manual for explicit VM testing before managed rollout.

Context

This is the additive side of the first Runneth-as-an-OS default package pass. The paired Agent Builder PR removes the same skills from the protected Runneth volume: https://github.com/Motion-Creative/agent-builder/pull/2319

The purpose of Phase One is to make high-confidence default Runneth behavior visible and package-installable, without changing the wording of the migrated behavior.

Research Grounding

The research supports keeping this first package narrow. The strongest live customization signals are not broad skill rewrites; they are customer-owned KPI rules, attribution windows, source-of-truth preferences, naming conventions, integration setup, and report/brief formats. Those become Phase 1.5 and Phase Two scope instead of being mixed into this migration-only package pass.

Validation

• node --test scripts/validate-runneth-package-index.mjs
• git diff --check
• Compared the copied skill files against the Agent Builder source versions before deletion

Notes

• The package is registered as manual, so managed sync can resolve it in the package plan without auto-installing it across baseline VMs.
• The broader catalog validator still has unrelated existing failures on this base branch: the runneth-classic catalog entry and add-roles-permissions metadata/version drift.