fix: Resolve linting issues in MCP integration

- Replace deprecated typing.Dict/List with built-in dict/list
- Fix boolean comparisons (== True/False) to direct checks
- Remove unused variables in demo script
- Update type annotations to use modern Python syntax

All pre-commit hooks should now pass.

apps/slack_rag.py

@@ -11,7 +11,6 @@ Usage:
 
 import argparse
 import asyncio
-from typing import List
 
 from apps.base_rag_example import BaseRAGExample
 from apps.slack_data.slack_mcp_reader import SlackMCPReader
@@ -121,7 +120,7 @@ class SlackMCPRAG(BaseRAGExample):
             print("4. Try running the MCP server command directly to test it")
             return False
 
-    async def load_data(self, args) -> List[str]:
+    async def load_data(self, args) -> list[str]:
         """Load Slack messages via MCP server."""
         print(f"Connecting to Slack MCP server: {args.mcp_server}")