- Introduce `upload_cog.py` for handling file uploads.
- Update AI model from `google/gemini-2.5-flash-preview` to `google/gemini-2.5-flash-preview-05-20` for improved performance and stability.
- Refine Teto's roleplay system prompt:
- Add explicit 18+ age disclaimer for all roleplay characters.
- Include context about prepended usernames for better AI understanding.
- Adjust Teto's perceived age to 18 for consistency.
- Remove outdated or unnecessary prompt instructions.
Rename the `roleplay_cog` to `neru_roleplay_cog` to align with the naming convention of other cogs and improve clarity. Update the cog loading list in `neru_bot.py` accordingly.
