Fix missing pagination in episode fetching for series with >500 episodes

[skilaky]

Summary

• GetSeriesEpisodesAsync() and GetEpisodeTvdbId() in TvdbClientManager.cs only fetched page 0 (first 500 episodes) from the TVDB v4 API
• For series with more than 500 episodes in a given season type (e.g. DVD order), episodes beyond page 0 were invisible to the plugin
• This caused incorrect season/episode assignments for long-running series

Root Cause

The TVDB v4 API returns a maximum of 500 episodes per page. Both methods had page: 0 hardcoded with no pagination loop. The same codebase already has working pagination in GetUpdates(), but it was never applied to episode fetching.

Example: Tatort (TVDB ID: 83214)

Tatort has 1,340 episodes in DVD order, spread across 3 API pages:

API Page	DVD Seasons	Episodes
Page 0	S1 – S51	500
Page 1	S52 – S72	500
Page 2	S72 – S96	340

Before fix: Episodes from seasons 52+ (pages 1-2) were invisible → 95% of episodes had wrong season/episode metadata.

After fix: All pages are fetched, all seasons are correctly mapped.

Changes

1. GetSeriesEpisodesAsync(): Added pagination loop to aggregate episodes from all pages into a single Data2 result (matching the existing GetUpdates() pattern)
2. GetEpisodeTvdbId(): Added pagination loop to iterate through pages until the requested episode is found

Affected Series

Any series with >500 episodes in a season type ordering, including:

• Tatort (1,340+ episodes in DVD order)
• The Simpsons (700+ episodes)
• Doctor Who (800+ episodes)
• And many other long-running series

Test Plan

• Verify Tatort (83214) in DVD order correctly maps episodes from seasons 52+ (previously broken)
• Verify series with <500 episodes still work correctly (no regression)
• Verify MissingEpisodeProvider creates correct virtual seasons for all pages
• Verify caching still works correctly with aggregated episode data

[Shadowghost]

Suggested change

	var allEpisodes = new List<EpisodeBaseRecord>(seriesResult.Data?.Episodes ?? Array.Empty<EpisodeBaseRecord>());
	var allEpisodes = new List<EpisodeBaseRecord>(seriesResult.Data?.Episodes ?? []);

Same for other places

[iampegram]

I think some of my code from #242 should be added into this, because the endpoint used in both places has a long-standing flaw where season-types 'altdvd' and 'alttwo' return no episodes even when there are.