Rollout Plan: phase in generated-app tests and default behavior

[snissn]

Background
We need a clean rollout path so generated-app tests ship without destabilizing existing users.

Scope

• Define rollout phases for generated-app tests:
  1. scaffold emission,
  2. contract tests emission,
  3. UI tests emission,
  4. generated CI template emission,
  5. making tests default-on.
• Add compatibility strategy for existing generated apps.
• Define deprecation timeline for any old testless paths.

Implementation details

• Update SPEC.md, AGENTS.md, and Readme.md to reflect rollout decisions.
• Provide migration notes for teams regenerating existing apps.
• Add acceptance checklist to PR template/release checklist.

Acceptance criteria

• Clear decision doc/checklist exists in-repo.
• Rollout order and defaults are unambiguous.
• Builder CI includes at least one generated-app test workflow verification before default-on switch.

[snissn]

Resolved by PR #37 (merged): rollout decision doc, SPEC/AGENTS/README alignment, PR template checklist, and release checklist added.