fix(action): surface raw invalid JSON output

[zerone0x]

Summary

Fixes #489.

When Gemini CLI emits non-JSON stdout/stderr, the action currently logs only generic warnings. This change prints the raw stream content directly into the step logs (capped to the first 200 lines) so the real failure is visible without downloading artifacts.

Changes

• add a small bash helper to surface raw non-JSON stdout/stderr in grouped logs
• wrap the raw output with GitHub's stop-commands guard so tool output cannot be interpreted as workflow commands
• keep the full logs in the existing artifacts and note when the inline preview is truncated

Testing

• Checking formatting...
  All matched files use Prettier code style!
• ran the helper locally with sample invalid output to verify the stop-commands/truncation behavior

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