Last of the three unified-tab phases. Surfaces the user's
persisted personalized playlists (decade mixes, hidden gems,
popular picks, daily mixes, discovery shuffle, etc.) on the
Sync page so they participate in the mirrored-playlist +
Auto-Sync pipeline like every other source.
Different shape from the LB / Last.fm tabs:
- Tracks already carry Spotify / iTunes / Deezer IDs (matched
at generation time from the discovery pool), so there is NO
MB-style "needs discovery" hop. The mirror is created with
fully-populated ``matched_data`` JSON inline, downstream
consumers (sync, wishlist) see canonical extra_data
immediately.
- Click on a card runs the kind's generator
(``POST /api/personalized/playlist/<kind>/<variant>/refresh``)
+ grabs the fresh track snapshot + mirrors under a synthetic
id of the form ``ssd_<kind>_<variant>`` (e.g. ``ssd_decade_1980s``,
``ssd_hidden_gems``). Re-clicks UPSERT the same row, so the
Auto-Sync schedule survives every refresh.
- Sub-tabs / archive concept don't apply here — each personalized
playlist is already a singleton per (profile, kind, variant);
the manager handles its own rotation.
New file: ``webui/static/sync-soulsync-discovery.js`` (~210 lines).
``initializeSyncPage`` learns a new tab branch. CSS adds
``soulsync-discovery-icon`` (star SVG, teal ``#14b8a6``) +
``.soulsync-discovery-playlist-card`` joins the unified card
selector group with a matching teal accent.
WHATS_NEW entry added under 2.6.3.
236 tests still green; no Python paths touched.
