fix: enforce durable bug fix verification workflow

[EvanProgramming]

Summary

• persist bounded bug-fix stages from reported through explained or blocked
• require observable reproduction, successful mutation, and successful verification receipts before success claims
• link every fix turn and explicit user feedback to workflow/task/attempt IDs and document recovery semantics

Validation

• make check
• make lint
• make test (104 tests)
• git diff --check
• fake-provider integration produced a real file and subprocess verification
• unsupported success had no side effect and was blocked
• failed verification and negative feedback were persisted and linked

Fixes #16