Refactor test scaffolding for capability and recursion suites

[mgomes]

Why

The capability and recursion tests had repeated engine/compile/call boilerplate, which made updates noisy and harder to audit.

This refactor centralizes common test setup while preserving behavioral assertions and coverage.

What changed

• Added shared test helpers for compile/call/error assertions.
• Migrated context/events/db/jobqueue/foundations capability tests to helper-based structure.
• Reduced repeated compile boilerplate in capability contract tests.
• Refactored recursion tests to helper-based setup.

Validation

• go test ./... (run after each atomic commit and once at the end)