chore: Remove unused MC_INACTIVE_HOURS config variable

This variable was defined but never used in the code.
Contact cleanup threshold is controlled directly in the UI.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -45,7 +45,6 @@ services:
       - MC_BRIDGE_URL=http://meshcore-bridge:5001/cli
       - MC_DEVICE_NAME=${MC_DEVICE_NAME}
       - MC_CONFIG_DIR=/root/.config/meshcore
-      - MC_INACTIVE_HOURS=${MC_INACTIVE_HOURS:-48}
       - MC_ARCHIVE_DIR=/root/.archive/meshcore
       - MC_ARCHIVE_ENABLED=${MC_ARCHIVE_ENABLED:-true}
       - MC_ARCHIVE_RETENTION_DAYS=${MC_ARCHIVE_RETENTION_DAYS:-7}