Favicon Fetch Triggers: Source Creation and Feed Success

What Was Built

• FaviconFetchJob trigger on manual source creation via SourcesController#create
• FaviconFetchJob trigger on successful feed fetch via SourceUpdater with cooldown check
• FaviconFetchJob trigger for each OPML-imported source with website_url
• End-to-end integration test: POST source -> enqueue -> perform -> verify attachment -> render show
• All triggers guard on ActiveStorage, favicons enabled, website_url present
• All triggers wrapped in rescue to never break the main flow

Files Modified

• app/controllers/source_monitor/sources_controller.rb -- added enqueue_favicon_fetch private method, called from create action
• lib/source_monitor/fetching/feed_fetcher/source_updater.rb -- added enqueue_favicon_fetch_if_needed with cooldown logic, called after update_source_for_success
• app/jobs/source_monitor/import_opml_job.rb -- added should_fetch_favicon? guard and enqueue call after each source.save
• test/controllers/source_monitor/sources_controller_favicon_test.rb -- 4 controller tests for create favicon trigger
• test/lib/source_monitor/fetching/feed_fetcher/source_updater_favicon_test.rb -- 8 unit tests for updater favicon trigger with guards
• test/jobs/source_monitor/import_opml_favicon_test.rb -- 3 tests for OPML import favicon trigger
• test/integration/source_monitor/favicon_integration_test.rb -- 3 integration tests for end-to-end flow