fix(deps): Raise google-adk and google-adk[eval] to >=2.7.0,<2.8.0.

[xgtcode]

Summary
This PR updates VeADK’s runtime dependency baseline so fresh installs can use the Google ADK session timestamp fixes introduced in ADK 2.7.x, while avoiding currently incompatible newer ADK lines.
Changes included:

• Raise google-adk and google-adk[eval] to >=2.7.0,<2.8.0.
• Keep agentkit-sdk-python>=0.8.5 flexible instead of pinning to a specific release.
• Keep opentelemetry-exporter-otlp>=1.37.0 flexible.
• Refresh uv.lock to resolve the compatible dependency line, currently google-adk==2.7.1.
• Add dependency metadata regression coverage.
• Add ADK 2.7 compatibility fixes for:
  • build graph serialization of VeADK nested sub_agents;
  • Studio lazy GenAI model loading under ADK 2.7 telemetry APIs.
• Update the runtime dependency compatibility PRD/spec in both English and Chinese.
• Fix a frontend TypeScript strict-mode issue in the WeCom authorization result callback.
  Why
  Users need google-adk>=2.7.0 because the relevant upstream session fixes are only available from ADK 2.7 onward:
• deterministic event reads;
• UTC storage/filtering for event timestamps.
  However, leaving google-adk>=2.7.0 without an upper bound currently resolves to newer ADK releases such as 2.11.0, where targeted compatibility tests fail due to upstream internal API changes. Therefore this PR intentionally sets the supported window to:
  google-adk>=2.7.0,<2.8.0
  Compatibility Notes
• Existing user constraints or lock files may still keep older dependency versions until refreshed.
• ADK 2.8+ is intentionally excluded for now and should be handled in a separate compatibility pass.
• Studio, sandbox, generated project, managed sidecar, and Docker dependency declarations are not broadly changed in this PR.