Add duplicate channel detection and cleanup preview

[rroy676]

Goal

Add duplicate channel detection and a safe cleanup preview so users can manage messy IPTV playlists without accidentally deleting useful channels.

Problem

Large IPTV playlists often contain many duplicates or near-duplicates, such as SD/HD/FHD variants, regional duplicates, multiple providers for the same channel, and VOD/series entries mixed into live TV.

Users need help identifying duplicates and choosing which versions to keep.

Expected behaviour

Add a duplicate detection/cleanup workflow that shows users what Stationarr found before making changes.

Possible duplicate signals:

- same channel name
- same normalized name
- same tvg-id / EPG ID
- same stream URL
- same group/category
- same logo
- quality suffixes such as SD/HD/FHD/UHD/4K

Suggested UI

Cleanup → Duplicates

Group: ESPN
- ESPN HD      Keep suggested
- ESPN SD      Disable suggested
- ESPN FHD     Alternative

[Apply selected changes]

Requirements

• Preview results before applying changes.
• Prefer disabling/excluding from output over destructive deletion.
• Let users manually choose which duplicate to keep.
• Allow rules such as prefer HD/FHD, prefer channels with EPG, prefer healthy streams.
• Handle large playlists with pagination/search.
• Avoid changing channels automatically without confirmation.

Validation

• Import a playlist with duplicate channels.
• Run duplicate detection.
• Confirm duplicates are grouped clearly.
• Apply a non-destructive cleanup action.
• Confirm generated output respects the selected changes.

Related

Related to #50 IPTV channel profiles, #53 stream/channel health checks, and #5 large playlist performance.