Deliver App Builder Golden showcase and closure slice

[kattsushi]

Outcome

Add the committed, root-excluded Todo Golden showcase and a non-mutating CI drift gate for the final App Builder Golden Monorepo slice.

Scope

• Generate and commit the canonical Todo showcase through the public generation boundary.
• Record provenance, canonical inputs, and a maintainer regeneration path.
• Prove root Nx and pnpm discovery exclude the showcase.
• Add a CI fixture and final acceptance matrix that detect drift without rewriting tracked artifacts.

Evidence

• SDD change: app-builder-golden-monorepo, tasks 8.1 and 8.2.
• Parent child branch: feat/app-builder-golden-nested-e2e at 1aa7977f9c42c903ba68418550315c9effdd88df.
• Tracker: feat(app-builder): track platform delivery #92.

[kattsushi]

Implemented in draft chained PR #130, targeting the public-generate prerequisite branch from PR #129.

Evidence recorded in the PR:

• public-CLI-generated canonical Todo fixture and provenance
• isolated CI drift checker that never rewrites the committed fixture
• strict-TDD showcase coverage and exact-parent affected lint/typecheck/test/build passing

This issue is not closed yet: PR #130 remains draft and must flow through the feature-branch chain and SDD verification.

[kattsushi]

Closing as not planned because Effectify App Builder has been retired in favor of contributing to lloydrichards/stack-effect. No App Builder implementation is retained on dev.