fix: recompute Season/Episode stable UUID after meta enrichment

[jackgdll]

Issue

• skipping media item with invalid UUID ... UUID mismatch errors logged after library refresh
• seasons/episodes mentioned in the errors never land in the DB, whole seasons of specials vanish.
• skipped item's id encodes a season one higher than the stored parent_idx (same IMDB anchor, episode number unchanged)

Cause

• AddonRuntime::refresh_meta re-derives the canonical UUID for Movie/Series only, not for Season/Episode.
• The recompute block's comment says: "Catalog stubs arrive with a TMDB-keyed UUID; validate() expects the canonical one", it just was never extended to seasons/episodes.

Fix

• addons/mod.rs: extend the UUID recompute to Movie | Series | Season | Episode, deriving the key via media.media_id_raw(), guarded on canonical().is_some().
• db/media.rs: regression tests for episode and series ids

I used Claude to debug and fix this then manually reviewed it and wrote the PR description myself

[jackgdll]

i'm not sure whether Person should also be supported here or not?

[lostb1t]

people are handled in a different location so this looks good