feat(stremio): prefer TVDB series search with IMDb fallback

[wrxco]

Summary

• prefer TvdbId queries for Stremio series searches when possible
• keep existing IMDb behavior as fallback when TVDB lookup fails or returns empty
• preserve current movie search path and existing Stremio output contract

What changed

• added resolveTVDBFromIMDb() in internal/api/tvdb_lookup.go using TVMaze lookup API
• updated handleStremioAddonStream to:
  • resolve IMDb -> TVDB for series
  • search Prowlarr with TvdbId first for tvsearch
  • fall back to ImdbId search on errors or empty TVDB result set
• refactored Prowlarr client search builder:
  • introduced searchWithID(...)
  • added SearchByTVDB(...)

Why

Some indexers behind Prowlarr support TV episode discovery only with TvdbId for tvsearch. Existing IMDb-only series queries return zero results in those setups.

Behavior notes

• no config migration required
• no breaking API/UI changes
• series search is now more compatible while retaining previous fallback behavior