Add discord-agent files and enable reply notifications

- Add discord_agent.py with reply() instead of send() for user notifications
- Add Discord bot Dockerfile and requirements.txt
- Add bot cogs (base_cog.py and integration_cog.py)
- Update .gitignore to track discord-agent directory
- Bot now replies to messages triggering notifications for users

discord-agent/Dockerfile

@@ -0,0 +1,10 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+CMD ["python", "discord_agent.py"]