Ambient-folders migration path #1607

Scenario

gh-aw is shipping ambient-folders which eliminates the artifact upload/download dance. Squad's shared component has 15+ lines of artifact management (upload workspace, download in agent jobs, re-upload on completion) that will become dead code once ambient-folders lands.

Early adopters on the preview will need to manually update their compiled locks. Teams that don't migrate will carry unnecessary complexity and may hit deprecation warnings.

Proposal

• Document the ambient-folders migration in Squad's gh-aw docs (what changes, what to remove, what stays)
• Provide a squad aw upgrade-component command or migration guide that rewrites the shared component to use the new syntax
• Detect ambient-folders availability at runtime and skip artifact steps automatically (graceful degradation)
• Add a deprecation notice to artifact-based paths once ambient-folders reaches GA

Value

Smooth upgrade path when gh-aw ships ambient-folders — no broken workflows.