Fix session report auth and reviewed ops continuation

[areshand]

Summary

• verify session-scoped worker bearer tokens in gateway mode rather than worker mode
• extract mode-aware worker token signing and verification with expiration/session tests
• restore the canonical ops role prompt and semantic envelope for fresh reviewed-ops continuation contexts

Production E2E findings

Thread github-thread-e2e-0827c exposed two independent blockers:

1. The session produced final-report.json, but the private report route returned 401 because gateway token verification was disabled outside worker mode.
2. After a successful reviewed github.read, the fresh ops continuation lacked canonical role grounding. Claude treated the local reviewed-ops protocol as fabricated prompt injection, became terminal, and could not prepare the required review-list operation.

The E2E was stopped after capturing both failures. No runbook, prod-mcp operation, secret, or architecture decision changes.

Validation

• control-server: 20/20 tests
• Rust: 59/59 tests
• full ./tests/run.sh, including mock orchestration E2E
• cargo fmt --check / formatted output
• git diff --check