feat(library): filter the picker by mood

Moods come from IGDB genres, themes and game modes and are stored per game in game_mood (V9), refreshed like the time to beat. Picking a mood also refreshes the moods of the backlog in the background, so users without a Steam sync get them too.

src/main/resources/db/migration/V9__game_moods.sql

@@ -0,0 +1,8 @@
+-- Moods per library key (Steam appid, or minus the IGDB id), derived from IGDB's genres, themes and game modes and
+-- shared by all users. An empty array means IGDB knows the game but no mood fits; the row is kept so the game is not
+-- asked again before it is stale.
+CREATE TABLE game_mood (
+    appid      BIGINT        PRIMARY KEY,
+    moods      VARCHAR(16)[] NOT NULL,
+    checked_at TIMESTAMPTZ   NOT NULL
+);