feat(plex): add Plex watchlist management functionality

[gwlsn]

Description

Add Plex watchlist support allowing users to add and remove movies and TV shows from their Plex watchlist directly from Seerr. I have included the button UI element on the Movie/TV show pages instead of the TitleCard (as is found in Jellyfin/Emby) as I find I more frequently want to add things to my Plex watchlist from that screen after seeing score/reviews and description. There is also a blacklist button there so I feel it fits with the overall design language.

The adding/remove from Plex watchlist relies on undocumented API calls as detailed here.

Backend Changes:

• Implement PlexTvAPI methods for watchlist operations
  • addToWatchlist() and removeFromWatchlist() using Plex Discover API
  • findPlexRatingKeyByTmdbId() with TMDB ID matching via metadata
  • isOnWatchlist() to check current watchlist status
  • Use fresh axios instance to avoid ExternalAPI header conflicts
• Add /api/v1/plex-watchlist endpoints (POST, DELETE, GET status)
• Implement duplicate prevention checking before adding items
• Add cache invalidation after watchlist modifications
• Extract ratingKey from Plex guid format (plex://movie/ID)
• Update OpenAPI spec with new Plex watchlist endpoints

Frontend Changes:

• Add Plex watchlist buttons to MovieDetails and TvDetails pages
• Position buttons between Blacklist and Trailer buttons
• Use unfilled amber star icon for add, filled amber star for remove
• Implement real-time watchlist status checking via useSWR
• Add state management for watchlist updates and loading states
• Add i18n support with tooltips for user guidance

This patch addresses request #2082

AI Disclosure

The majority of the code in this patch was generated by Claude Code with human supervision and revision. The above PR/Commit was also summarized by Claude Code.

How Has This Been Tested?

Tested locally with my personal Plex Media Server. Added and removed items from Plex watchlist through Seerr. Removed a watchlist item on Seerr that was added through official Plex app and vice versa to ensure compatibility with underlying Plex system. Tested with blacklisted and non-blacklisted items. As intended, button not visible on blacklisted item.

Screenshots / Logs (if applicable)

Checklist:

• [ x ] I have read and followed the contribution guidelines.
• [ x ] Disclosed any use of AI (see our policy)
• [ x ] I have updated the documentation accordingly.
• [ x ] All new and existing tests passed.
• [ x ] Successful build pnpm build
• [ x ] Translation keys pnpm i18n:extract
• [ N/A ] Database migration (if required)

EDIT: Updated to conform to new pull request template

[buzdriver]

Hi,
Not sure what happend here but I got like 50 re-requests of items already available from people that requested already requested material.
/BR

[gwlsn]

Hi, Not sure what happend here but I got like 50 re-requests of items already available from people that requested already requested material. /BR

Hi,

Thanks reporting this! This PR only adds the ability to manually add/remove items from your Plex watchlist via buttons on the movie/TV details pages. It adds a couple new endpoints but it doesn't interact with the request system, database, or the existing Plex watchlist sync job, so the re-requests you're seeing are likely unrelated to these changes.