Queue Separation -- Maintenance Queue - Source Monitor

What Was Built

Added dedicated maintenance queue for non-fetch jobs, keeping the fetch queue reserved for FetchFeedJob and ScheduleFetchesJob only. Configuration supports maintenance_queue_name (default: source_monitor_maintenance) and maintenance_queue_concurrency (default: 1, conservative for small servers). Seven jobs moved from :fetch to :maintenance queue. Tests verify all queue assignments.

Files Modified

lib/source_monitor/configuration.rb -- added maintenance_queue_name, maintenance_queue_concurrency attrs; extended queue_name_for/concurrency_for
app/jobs/source_monitor/source_health_check_job.rb -- :fetch -> :maintenance
app/jobs/source_monitor/import_session_health_check_job.rb -- :fetch -> :maintenance
app/jobs/source_monitor/import_opml_job.rb -- :fetch -> :maintenance
app/jobs/source_monitor/log_cleanup_job.rb -- :fetch -> :maintenance
app/jobs/source_monitor/item_cleanup_job.rb -- :fetch -> :maintenance
app/jobs/source_monitor/favicon_fetch_job.rb -- :fetch -> :maintenance
app/jobs/source_monitor/download_content_images_job.rb -- :fetch -> :maintenance
examples/advanced_host/files/config/solid_queue.yml -- added maintenance queue entry with comments
test/lib/source_monitor/configuration_test.rb -- 10 new tests for queue separation