Share the RD and TorBox initial-title search predicate

[ghbarker]

Real-Debrid and TorBox currently duplicate the rule that restricts hidden-provider source searches to part of the initial title. This extracts that identical predicate into one small, dependency-free helper while both screens retain their existing submit, empty-input, fetch and focus behavior.

Matching preserves the existing ASCII tokens, stopword fallback and substring behavior. For example, an initial title of The Matrix still permits prematrixed and rejects Unrelated only when both existing restriction flags apply.

Validation on webdav-sync at 75b53ef3:

• 12 tests through the mounted RD/TorBox search fields passed before extraction; 47 focused tests passed afterward.
• A mutation bypassing the predicate failed both hosts' guard assertions.
• Scoped analysis has no new diagnostics; all 72 existing host diagnostics match the unchanged baseline.

Independent of the other split PRs, including folder sorting. This draft replaces only the duplicated search-predicate portion of the retired aggregate #61. No provider registry, settings rearrangement, cache feature or UI redesign is included. Physical-device testing remains outstanding.