fix(brand): clean up remaining AgentAuth references

[devonartis]

Summary

• Renames stale current AgentAuth/agentauth product references to AgentWrit/agentwrit.
• Aligns TLS and mTLS compose cert mounts with scripts/gen_test_certs.sh by using /tmp/agentwrit-certs.
• Refreshes sec-l2b setup and S2/S3 evidence so current recorded output uses agentwrit identity/URN namespaces.
• Adds the CHANGELOG.md entry for this cleanup while preserving older historical AgentAuth entries.
• Bumps the pinned Go toolchain from go1.25.9 to go1.25.10 to resolve govulncheck standard-library findings in CI.

Verification

• PASS: strict post-grep leaves only CHANGELOG.md history and watchdog regexes.
• PASS: go test ./...
• NOTE: local ./scripts/gates.sh task is blocked by local toolchain setup: local golangci-lint 2.11.4 rejects the repo's current v1 config, and gosec is not installed. GitHub CI installs its pinned tools separately.
• NOTE: tests/sec-l2b/integration.sh could not run locally because Python cryptography is not installed. S2/S3 evidence was re-recorded against a live local broker using Node built-in Ed25519 crypto for the same challenge-response flow.

Refs #78

Do not merge until owner review is complete.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None