fix(agent-v2): restore keyboard access to row actions

[lyzno1]

Summary

• keep configurable row actions in the keyboard tab order while visually hidden
• reveal actions on hover or focus without reserving layout space
• remove the class-level test that encoded the inaccessible display behavior

Testing

• pnpm -C web test features/agent-v2/agent-detail/configure/components/orchestrate/knowledge/tests/index.spec.tsx --run
• pnpm -C web exec eslint features/agent-v2/agent-detail/configure/components/orchestrate/common/configurable-item.tsx features/agent-v2/agent-detail/configure/components/orchestrate/knowledge/tests/index.spec.tsx
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.47%. Comparing base (6e5ba18) to head (ba23797).

Files with missing lines	Patch %	Lines
...omponents/orchestrate/common/configurable-item.tsx	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #38792   +/-   ##
=======================================
  Coverage   85.47%   85.47%           
=======================================
  Files        5025     5025           
  Lines      273457   273457           
  Branches    51259    51259           
=======================================
  Hits       233729   233729           
  Misses      35238    35238           
  Partials     4490     4490           

Flag	Coverage Δ
dify-ui	94.61% <ø> (ø)
web	85.15% <50.00%> (ø)

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