fix: harden OpenCode planner runtime contract

[Grzanka777]

Summary

• enforce evidence-first planning before Proceed
• require live repository facts and VERSION inspection
• add mandatory manual-vs-agent routing
• correct validation, artifact-path, and Decision Package rules
• update planner tests and current README test count

Validation

• ruff format --check: pass
• ruff check: pass
• mypy: pass
• pytest: 78 passed
• git diff --check: clean
• independent review: PASS
• staging audit: PASS

Safety

• no mechanical-agent changes
• no shared contract changes
• no VERSION change
• no Oracle Wisdom changes
• no Codex changes
• no Brain write