feat(slint, core): per-artist play history feeds the discovery filter

Ports the minimum of src-tauri/src/reco_store needed to honour the
"skip artists I already listen to" gate in the discovery pipeline.

play_history (`crates/qbz-slint/src/play_history.rs`):
  - Tiny SQLite store at <data-dir>/qbz/play_history.db with WAL
    (ADR-002), holding play_events (artist_id + occurred_at, one row
    per audible track start) and artist_names (id -> name upsert).
    Lazy open, errors collapsed to log::warn so a missing DB just
    means an empty filter — same default Tauri lands on a fresh
    profile.
  - record_play(artist_id, name) wired into playback::record_recent
    so every audible track start increments the per-artist count.
  - known_artists(threshold) returns the (HashSet<u64>,
    HashSet<String>) pair Tauri's filter expects — qobuz ids for
    suppressing validated matches, normalized names for suppressing
    MB candidates upstream.

qbz-core::musicbrainz_discover_artists:
  - New `known_artists` closure parameter, called once per
    invocation. Threshold matches Tauri (>2 plays).
  - Filter applied at both stages: MB candidates dropped when their
    normalized name is in known_names; Qobuz matches dropped when
    their id is in known_ids (mirrors local_known_qobuz_ids check
    in v2_get_discovery_artists).

The Tauri reco_store has many other features (favorites, top
genres, home seeds) the Slint shell does not use yet — those stay
out of this commit; only the play-count surface needed by the
sidebar's "You may also like" filter is ported.

cc

crates/qbz-slint/Cargo.toml

@@ -38,6 +38,7 @@ qbz-audio = { path = "../qbz-audio" }
 qbz-core = { path = "../qbz-core" }
 qbz-models = { path = "../qbz-models" }
 qbz-integrations = { path = "../qbz-integrations" }
+rusqlite = { version = "0.31", features = ["bundled"] }
 qbz-cache = { path = "../qbz-cache" }
 qbz-credentials = { path = "../qbz-credentials" }