fix(lark): emit card v2 callback buttons

[eanzhao]

Summary

• Render Lark/Feishu Card JSON 2.0 buttons directly in body.elements instead of the legacy action.actions wrapper.
• Move button callback payloads from top-level value to behaviors[0].value, matching Card JSON 2.0 while preserving the existing NyxID card.action.trigger parsing contract.
• Update form card rendering and tests so form inputs/buttons use the same v2 shape.

Root Cause

/agents still produced a hybrid card after PR #419: the card body was moved under body.elements, but buttons kept the older container/value shape. Lark rejected the interactive reply through NyxID with channel-relay/reply -> 502, and the single-use relay token prevented text fallback.

Validation

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.39%. Comparing base (cf44747) to head (0c27dbc).
⚠️ Report is 2 commits behind head on dev.

@@            Coverage Diff             @@
##              dev     #422      +/-   ##
==========================================
- Coverage   70.39%   70.39%   -0.01%     
==========================================
  Files        1175     1175              
  Lines       84460    84460              
  Branches    11126    11126              
==========================================
- Hits        59456    59452       -4     
- Misses      20714    20718       +4     
  Partials     4290     4290              

Flag	Coverage Δ
ci	70.39% <ø> (-0.01%)	⬇️

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see 3 files with indirect coverage changes

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep form buttons from emitting open_url behavior

When a card enters form mode (TextInput present), every non-input action is rendered by BuildFormButton, which always sets form_action_type to submit. This new branch returns an open_url behavior for ActionElementKind.Link, so a link inside a form now gets mixed semantics (submit + open_url), which can prevent the expected callback/form submission flow (or cause card validation rejection) for any workflow that combines text inputs with a link action. Please gate this branch for non-form buttons or suppress form_action_type for link actions.

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