feat: Refactor gemini-cli workflow for flexible, context-aware execution (#116)

This commit refactors the gemini-cli workflow to be more flexible and
context-aware. The previous plan-based system has been replaced with a
more dynamic approach.

  Key changes include:

- Removed the stateful plan# comment parsing and REQUEST_TYPE logic from
the workflow YAML. This significantly simplifies the workflow
definition.

- Added new steps to gather the full context of an issue or pull
request, including its description and all associated comments. This
information is now passed directly to Gemini CLI.

- Updated the core prompt to instruct the AI to act as a more
general-purpose assistant. It is now responsible for creating and
maintaining its own execution plan via a checklist in the GitHub
comments.

This new design makes the interaction more natural and less dependent on
the prior planning workflow.

cc @galz10

Author: jerop