Add root / index endpoint to fix 404 on GET /

Problem

The API server registers /health and many /api/* routes, but no route for /. Any request to the server root therefore falls through to Flask's default 404:

2026-10-21 16:05:59 - werkzeug - 127.0.0.1 - "GET / HTTP/1.1" 404 -
2026-10-21 16:06:04 - werkzeug - 192.168.1.119 - "GET / HTTP/1.1" 404 -

This is the first URL a user (or a browser on the LAN) hits after starting the server, so it looks like the server is broken even though /health returns 200.

Fix

Adds a GET / index endpoint that returns basic service info (name, version, status, port) plus the list of registered endpoints, so the root URL is self-documenting:

{
  "name": "HexStrike AI Tools API Server",
  "version": "6.0.0",
  "status": "running",
  "port": 8888,
  "message": "HexStrike AI API is running. See /health for tool status.",
  "endpoints_count": 173,
  "endpoints": ["/", "/api/ai/generate_payload", ...]
}

Testing

• GET / -> 200 (was 404)
• GET /health -> 200 (unchanged)
• Verified from both 127.0.0.1 and a LAN client (192.168.1.119)

Only adds a new route; no existing behaviour is changed.