docs(plex): refresh watch-sync job docstrings for Plex-authoritative pull (S2)

The incremental/reconcile job docstrings still described last-write-wins and a
30-min cadence; update them to match the S2 behavior (Plex wins on divergence,
15-min incremental) so the "why" doesn't drift from the code.

backend/app/plex/watch_sync.py

@@ -432,10 +432,11 @@ def _repush_dirty(db: Session, plex: PlexClient, link: PlexLink) -> int:
 
 
 def run_plex_watch_sync(db: Session) -> dict:
-    """Scheduler job (default 30 min) — the cheap incremental pass. Pulls Plex-side changes since the
-    high-water mark (watch history + on-deck, filtered to the owner account) into Siftlode under
-    last-write-wins, then re-pushes any still-unsynced local states. Does NOT propagate un-watches
-    (the history feed only carries positive views) — that's `run_plex_watch_reconcile`'s job."""
+    """Scheduler job (default 15 min) — the cheap incremental pass. Pulls Plex-side changes since the
+    high-water mark (watch history + on-deck, filtered to the owner account) into Siftlode, resolving a
+    divergence to Plex (the source of truth — see `_pull_apply`), then re-pushes any still-unsynced
+    local states. Does NOT propagate un-watches (the history feed only carries positive views) — that's
+    `run_plex_watch_reconcile`'s job."""
     if not sysconfig.get_bool(db, "plex_enabled"):
         return {"skipped": "disabled"}
     total = {"links": 0, "watched": 0, "in_progress": 0, "repushed": 0}
@@ -486,7 +487,7 @@ def run_plex_watch_sync(db: Session) -> dict:
 def run_plex_watch_reconcile(db: Session) -> dict:
     """Scheduler job (default daily) — the authoritative full reconcile. Rescans every section and,
     per item, uses `synced_to_plex` to settle what the incremental feed can't:
-      - Plex has a state, Siftlode differs → last-write-wins (Plex usually the newer here).
+      - Plex has a state, Siftlode differs → Plex wins (the source of truth — see `_pull_apply`).
       - Siftlode has a state, Plex has NO record:
           · synced_to_plex=True  → Plex un-watched it since our last sync → clear it (un-watch).
           · synced_to_plex=False → a local change that never reached Plex → re-push it (via