fix: scan records the probed format + skips hidden album dirs (probe once)

Probe each album exactly once and thread the ProbeResult through for
tags, quality, and format instead of hardcoding LibraryItem.format to
"FLAC" and re-probing on the tag-fallback path. Also skip album-level
directories starting with "." (previously only artist-level dirs were
skipped).

worker/tests/test_scan.py

@@ -96,3 +96,24 @@ def test_scan_is_idempotent(conn, tmp_path):
     second = scan_library(conn, resolver, FakeProbe(quality_class=3), dest_root=str(tmp_path))
     assert second.imported == 0  # already recorded
     assert _counts(conn) == {"LibraryItem": 1, "MonitoredRelease": 1, "WatchedArtist": 1}
+
+
+def test_scan_records_the_probed_format(conn, tmp_path):
+    _album(tmp_path, "John Mayer", "Sob Rock (2021)")
+    resolver = FakeResolver({
+        ("John Mayer", "Sob Rock"): MBTarget(
+            artist="John Mayer", album="Sob Rock", year=2021, rg_mbid="rg2", artist_mbid="a1"),
+    })
+    scan_library(conn, resolver, FakeProbe(fmt="MP3", quality_class=1), dest_root=str(tmp_path))
+    with conn.cursor() as cur:
+        cur.execute('SELECT format, "qualityClass" FROM "LibraryItem" WHERE album=%s', ("Sob Rock",))
+        assert cur.fetchone() == ("MP3", 1)  # the probed format is recorded, not a hardcoded FLAC
+
+
+def test_scan_skips_hidden_album_dirs(conn, tmp_path):
+    hidden = tmp_path / "John Mayer" / ".sync"
+    hidden.mkdir(parents=True)
+    (hidden / "01 Track.flac").write_bytes(b"")
+    result = scan_library(conn, FakeResolver({}), FakeProbe(), dest_root=str(tmp_path))
+    assert (result.imported, result.skipped) == (0, 0)  # hidden album dir not scanned
+    assert _counts(conn) == {"LibraryItem": 0, "MonitoredRelease": 0, "WatchedArtist": 0}