revert(ai): remove SUPERVISOR_LOGFILE env var from supervisor-ui

Supervisor XML-RPC API v3.0 (Supervisor 4.3.0) only supports 2-parameter
readLog(offset, length) calls, not 3-parameter calls with filename.
The SUPERVISOR_LOGFILE environment variable is not used by the API.

Testing showed:
- Working: server.supervisor.readLog(-4096, 0)
- Failing: server.supervisor.readLog(-4096, 4096, '/path/to/log')

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

ai/compose.yaml

@@ -246,7 +246,6 @@ services:
       # Connect to RunPod Supervisor via Tailscale
       SUPERVISOR_HOST: ${GPU_TAILSCALE_IP}
       SUPERVISOR_PORT: ${SUPERVISOR_BACKEND_PORT:-9001}
-      SUPERVISOR_LOGFILE: /workspace/logs/supervisord.log
       # No auth needed - Supervisor has auth disabled (protected by Authelia)
     networks:
       - compose_network