Smart slideshow clustering for Immich

[artyfarty]

Hey, i'm not sure how useful / fitting this PR as is, and the settings that regulate this sort system may not be very intuitive for broader audience. Concept is mine, implementaion - entirely vibe coded, but it seems to work well for my case. Feel free to review it, or just reuse the concepts in future versions.

Summary

Adds an optional Smart slideshow mode for the Immich provider that evens out playback when you've selected a mix of single-day event albums and long-span collection albums.

The problem this solves: with the current flat random, a 1000-photo vacation album drowns out a 50-photo themed collection because randomization has no notion of "one event = one moment". Burst sequences (several shots seconds apart) further compound the issue by occupying consecutive slideshow slots with near-duplicate frames.

What it does

Inside the Immich provider, before mapping assets to AerialMedia:

1. Temporal clustering. Sort by localDateTime, group consecutive assets when the gap is below a user-configurable threshold (default 30 min, options 1/10/30/60/360/1440). One random representative per cluster survives into the playlist. Clusters get re-randomized each fetch, so across sessions the user still sees the non-representative frames.
2. Optional exempt regex. Albums whose names match a user-supplied regex bypass clustering — useful for scanned film where dateTimeOriginal reflects the scan session, not the actual shoot time, and would collapse an entire roll into one slot. Default empty (opt-in).
3. Exempt keep-percent. Even with exempt, user can dampen exempt-album airtime via a random subsample (25/50/75/100%). Default 100%.

All three knobs live under a new "Smart slideshow" PreferenceCategory on the Immich source screen. Feature is off by default — existing playback behaviour is unchanged for anyone who doesn't opt in.

Files

• providers/immich/ImmichClusterer.kt — the algorithm (pure, ~90 LOC, testable)
• providers/immich/ImmichMediaProvider.kt — call site, gates on new pref
• models/prefs/ImmichMediaPrefs.kt — three new prefs
• res/xml/sources_immich_videos.xml — new PreferenceCategory
• res/values/arrays.xml + strings.xml — UI strings and entries

Test plan

• Leave the feature off → media count and playback identical to current master.
• Enable with gap=30 → verify large single-day albums are represented by ~N/density clusters, not by every frame.
• Enable with exempt regex matching a known burst-sensitive album → that album's assets bypass collapse; non-matching albums still collapse normally.
• Exempt keep-percent = 50 → roughly half of exempt assets drop out (random).
• Verify no crash when an asset lacks localDateTime (falls through to a separate un-dated bucket, returned verbatim).
• Fetch → force refresh → representatives differ across runs (re-randomization works).

Notes

Scope kept intentionally narrow to the Immich pipeline. The clusterer is a pure function and safe to ignore for other providers. A follow-up PR will add DATE_TIME_TAKEN and SOURCE_POOL overlay tags + optional periodic playlist refresh (see #TBD).

[artyfarty]

P.S. i will rpobably iterate on this project more in following days as i accumulate experience on how well it works. When developing we were creating simulated sets as webpages to find usable clusterisation parameters. Maybe i'll make it so every display of a slot uses random member of the cluster. Also i already implemented an auto refresh in another branch, because slideshow may run for weeks on my TV.

Anyway, feedback will be appreciated.

[artyfarty]

Added in-slot randomizer