Loosen approximate matching and link to the album version's folders

Matching:
- Prefer the studio album over singles, EPs and compilations when a song
  exists on several releases, including when the master also has the
  single at the slave's exact folder.
- Ignore release labels (Single Version, Remastered, Explicit, Deluxe)
  inside brackets or a trailing " - ..." part; "Clean" stays a version.
- Treat live/acoustic/remix/... album folders as different recordings;
  the strict top-folder fallback now respects this too.
- Add a last-resort library-wide search that only accepts candidates whose
  artist tag agrees with the slave file.

Linking:
- Cross-folder matches now mirror the master's path in the slave (e.g. a
  single moves into the album folder) and prune the emptied folder; a
  "keep in current folder" option preserves the old behaviour. Undo
  recreates and prunes folders accordingly.
- Operations record the match kind and reason, so undo (and promotes that
  rename the master file) restore the correct pairing instead of leaving
  the file unmatched until the next scan.

UI: rewrite the approximate matching description with Avenged Sevenfold
examples and clear safeguards, and show where linking will place a file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -20,15 +20,32 @@ path on both sides. The fallbacks below catch small differences, and a scan warn
 | Same title, **different format** (`Song.mp3` vs `Song.flac`) | Status `similar` (other format). Manual review. |
 | Same title after ignoring track numbers/punctuation (`01 - Song!.flac` vs `Song.mp3`) | Status `similar` (similar title). Manual review. |
 | Same top-level folder and title, but a **different subfolder** | Status `similar` (same top folder, other subfolder). Manual review. |
-| *(opt-in)* **Approximately** the same title, disc folders ignored (`Cats/Disc 02/07 Memory.flac` vs `Cats/07 Memory.mp3`) | Status `similar` (approximate match), with the reason shown. Manual review. |
+| *(opt-in)* Approximately the same song in another folder, e.g. a **single vs. the album version** or a **disc folder** | Status `similar` (approximate match), with the reason shown. Manual review. |
 | Only exists in the slave library | Status `unmatched`. Never touched. |
 | Already the same inode | Status `linked`. |
 
-**Approximate matching** is an opt-in setting on each pair. For slave files the strict rules could not place, it searches the same
-album with disc folders (`Disc 02`, `CD2`, …) ignored, then the whole top-level folder, and compares titles by similarity against a
-threshold you choose (85% by default; a matching track number adds a small bonus). Several guards keep it from linking the wrong song:
-version words such as *Live*, *Remix*, *Reprise* or *Instrumental* must agree on both sides, a file is left unmatched when two
-candidates are nearly tied, and approximate matches never auto-link.
+**Approximate matching** is an opt-in setting on each pair. It finds songs whose file name or folder doesn't line up exactly with the
+master library and recommends linking them to the master's album version:
+
+| Case | Slave | Master |
+|---|---|---|
+| Single → album version | `Avenged Sevenfold/Hail to the King - Single/Hail to the King.mp3` | `Avenged Sevenfold/Hail to the King/01 Hail to the King.flac` |
+| Disc folders ignored | `Avenged Sevenfold/Nightmare/04 Buried Alive.mp3` | `Avenged Sevenfold/Nightmare/Disc 1/04 Buried Alive.flac` |
+| Small title differences | `Avenged Sevenfold/City of Evil/Bat Country (Remastered).mp3` | `Avenged Sevenfold/City of Evil/03 Bat Country.flac` |
+
+It searches the same album first (disc folders ignored), then the artist's other albums, then, as a last resort, the whole master
+library. Titles are compared by similarity against a threshold you choose (85% by default), and release labels such as *Single
+Version*, *Remastered* or *Explicit* are ignored. When a song exists on several releases, the studio album wins over singles, EPs
+and compilations, even if the master library also has the single. Linking such a match places the file at the master's path in the
+slave library (the emptied single folder is removed), or you can keep it in the slave's current folder.
+
+Safeguards:
+
+- Different recordings never match. *Live*, *Remix*, *Acoustic*, *Instrumental* and similar versions are kept apart, including
+  whole live or acoustic albums.
+- Matches found outside the artist's folder require both files' artist tags to agree.
+- Ambiguous candidates are skipped rather than guessed.
+- Approximate matches are never linked automatically.
 
 **Manual review** shows both files side by side and ranks their quality: lossless beats lossy, then bit depth and sample rate, then
 codec-weighted bitrate (Opus and AAC count for more per kbps than MP3). You then have three choices: