Initial implementation of Music Metadata Enricher

AI-powered per-album pipeline: scan → local hints → MusicBrainz/Discogs/Claude
resolve → cover art → interactive or auto review → tag write + rename + report.
All external dependencies optional; 17/17 unit tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

models.py

@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Optional, List, Dict
+
+
+AUDIO_EXTENSIONS = {
+    ".mp3", ".flac", ".m4a", ".aac", ".ogg", ".opus",
+    ".wav", ".wma", ".aiff", ".ape",
+}
+IMAGE_EXTENSIONS = {".jpg", ".jpeg", ".png", ".webp", ".bmp", ".gif"}
+TRACKLIST_EXTENSIONS = {".txt", ".htm", ".html", ".nfo"}
+PLAYLIST_EXTENSIONS = {".m3u", ".m3u8", ".pls"}
+
+
+@dataclass
+class ScannedFile:
+    path: Path
+    kind: str  # "audio" | "image" | "tracklist" | "playlist" | "other"
+
+
+@dataclass
+class AlbumScan:
+    album_dir: Path
+    audio_files: List[Path] = field(default_factory=list)
+    image_files: List[Path] = field(default_factory=list)
+    tracklist_files: List[Path] = field(default_factory=list)
+    other_files: List[Path] = field(default_factory=list)
+
+
+@dataclass
+class TrackHints:
+    path: Path
+    track_number: Optional[int] = None
+    disc_number: Optional[int] = None
+    title: Optional[str] = None
+    artist: Optional[str] = None
+    duration: Optional[float] = None
+    existing_tags: Dict[str, str] = field(default_factory=dict)
+
+
+@dataclass
+class AlbumHints:
+    album_dir: Path
+    dir_artist: Optional[str] = None
+    dir_album: Optional[str] = None
+    dir_year: Optional[str] = None
+    tracklist_text: Optional[str] = None   # merged text from all tracklist files
+    cover_images: List[Path] = field(default_factory=list)
+    tracks: List[TrackHints] = field(default_factory=list)
+
+
+@dataclass
+class TrackProposal:
+    path: Path
+    title: str
+    artist: str
+    track_number: Optional[int]
+    disc_number: Optional[int]
+    new_filename: Optional[str] = None   # only set when --rename is active
+    mbid: Optional[str] = None
+
+
+@dataclass
+class AlbumProposal:
+    album_dir: Path
+    album: str
+    albumartist: str
+    date: Optional[str]
+    genre: Optional[str]
+    label: Optional[str]
+    mbid: Optional[str]               # MusicBrainz release ID
+    cover_path: Optional[Path]        # resolved local or downloaded cover
+    cover_source: Optional[str]       # "local" | "musicbrainz" | "discogs"
+    tracks: List[TrackProposal]
+    confidence: float
+    sources: List[str] = field(default_factory=list)
+    notes: List[str] = field(default_factory=list)