Docs: lock ephemeral Fargate CSS serve contract #172

Parent

#171

What to build

Lock the stretch contract in Git: feature spec, ADR-0004, and links from the Friday MUST guide / credit docs index / chapter-5 pointers so operators know local rehearsal stays MUST and AWS up-down is stretch.

Acceptance criteria

• Feature spec aws-fargate-serve-demo exists in English with problem/solution/stories/decisions/testing/out of scope
• ADR-0004 accepted describing first platform/ slice (ephemeral Fargate CSS serve)
• Friday demo guide stretch line points at the feature spec
• No AWS vocabulary added to credit/CONTEXT.md

Blocked by

None - can start immediately.