fix Keep season context when playing specials displayed inline in a seaon

[KevOutIngs]

Pull Request

Summary

A special with AirsBefore/AirsAfter metadata is displayed inside a regular
season once the library has DisplaySpecialsWithinSeasons enabled, but the item
still carries Specials as its own SeasonId. Opening such a special from a
season reloaded the detail screen against Specials, and playing it queued the
Specials season rather than the run that was on screen.

This carries the browsed season through navigation and playback so an inlined
special stays in the season that actually lists it.

Related Issues

• Closes #
• Fixes #
• Related to #

Type of Change

• Bug fix
• New feature
• Refactor
• Performance improvement
• UI/UX update
• Documentation update
• Build/CI change
• Other (describe):

Changes Made

• Links carry the browsed season as a seasonContext query parameter, so the
  detail screen loads the list the viewer came from and falls back to the item's
  own season when that list does not contain it.
• Playback queues the season that actually lists the episode rather than the
  special's own SeasonId.
• A queue's season is resolved from its regular episodes instead of the completed
  item, so the rollover after an inlined special continues into the correct season.
• A season list mixing specials with regular episodes keeps the server's aired
  order; sorting by season number would drag a special to the front of the run it
  was placed in.
• Playing an episode from a season screen queues the rest of that season instead
  of stopping after the single item.
• New lib/util/season_queue_context.dart consolidates season/queue resolution
  that was previously duplicated in playback_module.dart (net −90 lines there).

Platform

• Android
• iOS
• tvOS
• Web
• macOS
• Windows
• Linux
• All / Shared code

Testing

Unit tests cover the season/queue resolution logic; the app was built and
launched on macOS to confirm the branch compiles and runs.

• Tested on emulator / simulator
• Tested on physical device
• Manual testing completed
• Not tested (explain why):

Test Steps

1. Enable DisplaySpecialsWithinSeasons on a TV library whose series has a
   special with AirsBefore/AirsAfter metadata.
2. Open the season and confirm the special appears at its aired position (not
   pulled to the front of the season).
3. Open the special: the episode list shown must remain the browsed season, not
   Specials.
4. Play the special: playback must continue into the next episode of that season.
5. Play through to the season's last episode and confirm rollover moves into the
   next season.
6. Open a special from the Specials season directly and confirm it still behaves
   as part of Specials.

Screenshots (if applicable)

N/A — no visual changes; behaviour only.

Checklist

• Code builds successfully
• Code follows project style and conventions
• No unnecessary commented-out code
• No new warnings introduced