[codex] Fix Lark v2 card schema

[eanzhao]

Problem and solution

Fixes #416.

Lark schema 2.0 interactive cards require renderable card blocks under body.elements. The standard LarkMessageComposer interactive-card path still emitted elements at the root, producing a hybrid v1/v2 payload that NyxID forwards to Lark and can fail with a 502 for /agents and other card-only replies.

This PR changes the standard interactive-card branch to emit body.elements, matching the existing form-mode branch and Lark v2 shape.

Impact paths

• agents/platforms/Aevatar.GAgents.Platform.Lark/LarkMessageComposer.cs
• test/Aevatar.GAgents.Platform.Lark.Tests/LarkMessageComposerTests.cs

NyxID cross-check

Checked the local NyxID repository at ~/Code/NyxID:

• backend/src/services/channel_adapters/lark.rs passes reply.metadata.card through as the interactive Lark content string.
• The send path posts that content to /open-apis/im/v1/messages with msg_type = "interactive".
• Existing NyxID card body tests still cover the older root-level elements shape, so this repository needs to produce the valid Lark v2 body.elements payload before handing it to NyxID.

No NyxID code change is included in this PR; the issue's timeout/schema-validation hardening remains a separate defense-in-depth follow-up.

Validation

• dotnet test test/Aevatar.GAgents.Platform.Lark.Tests/Aevatar.GAgents.Platform.Lark.Tests.csproj --nologo - passed, 13 tests
• dotnet test test/Aevatar.GAgents.ChannelRuntime.Tests/Aevatar.GAgents.ChannelRuntime.Tests.csproj --nologo - passed, 421 tests
• bash tools/ci/test_stability_guards.sh - passed
• git diff --check - passed

Docs

No architecture or user-facing documentation changes were needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.37%. Comparing base (f5cc284) to head (87568b6).
⚠️ Report is 2 commits behind head on dev.

@@            Coverage Diff             @@
##              dev     #419      +/-   ##
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- Coverage   70.38%   70.37%   -0.01%     
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  Files        1175     1175              
  Lines       84453    84453              
  Branches    11124    11124              
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- Hits        59440    59438       -2     
- Misses      20721    20723       +2     
  Partials     4292     4292              

Flag	Coverage Δ
ci	70.37% <ø> (-0.01%)	⬇️

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