feat(rss): prioritize custom name for TMDB lookup

[sw1313]

Summary

• use a non-empty custom RSS name as the TMDB lookup title for non-aggregate subscriptions
• preserve the parsed torrent title fallback for blank names and aggregate feeds
• keep title_raw unchanged and add focused analyser coverage

Closes #1061

Test plan

• pytest src/test/test_rss_analyser.py src/test/test_api_rss.py src/test/test_rss_engine_new.py -q
• ruff check src/module/rss/analyser.py src/test/test_rss_analyser.py

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