chore(deps): upgrade Google ADK to 2.6.1

[fmind]

What

• raise the Google ADK runtime minimum from 2.6.0 to 2.6.1
• refresh the exact uv lock artifact and hashes

Why

Exact-main freshness run 30671450837 detected that Google ADK 2.6.1 became stable after the v0.5.0 candidate locked 2.6.0. The patch fixes consumed tool-confirmation revalidation, which is directly relevant to the course's guarded-action boundary.

The published 2.6.1 metadata retains mcp<2 and OpenTelemetry <=1.42.1, so the repository's compatibility holds remain accurate.

How

The change is intentionally limited to the direct minimum and the resolver-produced lock entry. The installed 2.6.1 wheel preserves the Runner constructor seam used by the governed evaluation adapter.

Test plan

• installed wheel metadata and Runner signature inspected
• 153 focused action, evaluator, governance, MLflow, server, smoke, and telemetry tests
• mise run format
• mise run check
• mise run test — 630 passed, 95.53% branch coverage
• mise run scan
• mise run build — agent image contains google-adk==2.6.1

Exact-head acceptance

• CI 30672163673, Docs 30672163697, Scan 30672163616, and CodeQL 30672162272 green
• Platform 30672179175 green, including isolation, load, telemetry, backup/restore, and teardown
• Eval 30672179125 green with all six signals; sanitized evidence independently validated against the exact SHA and lock
• Freshness 30672542504 green with zero findings and no collection warnings