Revert "Add siGit Code"

[anna239]

Reverts #239

revert because of

Failed tests:
  - sigit (binary): Error during auth check: ValueError: ACP spec violation: agent wrote non-JSON to stdout: 'general.architecture: qwen3'
Per the ACP spec, agents MUST NOT write anything to stdout that is not a valid ACP message. Diagnostic output should go to stderr.
  - sigit (npx): Error during auth check: ValueError: ACP spec violation: agent wrote non-JSON to stdout: 'general.architecture: qwen3'
Per the ACP spec, agents MUST NOT write anything to stdout that is not a valid ACP message. Diagnostic output should go to stderr.

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