refactor(product-domains): add runtime facade guardrails

[limityan]

Summary

• Add product-domain runtime facade contracts for MiniApp lifecycle-state persistence and function-agent Git/AI orchestration readiness.
• Delegate only MiniApp storage-backed lifecycle persistence from core through the new facade while keeping compile/source reads, worker execution, host dispatch, built-in seeding, Git/AI calls, prompt templates, JSON extraction, and concrete error mapping core-owned.
• Add core function-agent AI adapter shape without rewiring existing product execution paths.
• Refresh boundary checks and architecture/module guidance so future runtime migration requires explicit port/provider design and equivalence tests.

Functional Boundary

This PR is intended to be behavior-preserving. It does not move MiniApp worker/runtime execution, built-in MiniApp update logic, function-agent product call paths, tool runtime ownership, or product-surface UI/protocol behavior. The code changes focus on ownership seams and regression coverage around existing behavior.

Validation

• node scripts/check-core-boundaries.mjs
• cargo test -p bitfun-product-domains --no-default-features
• cargo test -p bitfun-product-domains --features product-full
• cargo check -p bitfun-core --features product-full
• cargo test -p bitfun-core miniapp::manager::tests -- --nocapture
• cargo test -p bitfun-core function_agents:: -- --nocapture
• cargo tree -p bitfun-product-domains --no-default-features --depth 1 --edges features
• git diff upstream/main --check