Scheduler Config Exposure

What Was Built

• scheduler_batch_size (default 25) and stale_timeout_minutes (default 5) added to FetchingSettings
• Scheduler.run reads batch size and stale timeout from config instead of hardcoded constants
• StalledFetchReconciler.default_stale_after reads from config with fallback
• 4 new tests + existing tests updated for 5-min default; 16 tests pass, 0 failures

Files Modified

• lib/source_monitor/configuration/fetching_settings.rb — added 2 attr_accessors + defaults
• lib/source_monitor/scheduler.rb — wired to config, added stale_timeout method
• lib/source_monitor/fetching/stalled_fetch_reconciler.rb — reads config instead of Scheduler constant
• test/lib/source_monitor/scheduler_test.rb — 4 new tests, updated constant refs