Redo file naming in the style of Lidarr and add "Rename now"

Naming: separate artist folder, album folder, track and multi-disc track
formats with presets, Lidarr-style tokens ({Artist Name}, {Artist
NameThe}, {Artist CleanName}, {Artist NameFirstCharacter}, {Album
Title}, {Album TitleThe}, {Album CleanTitle}, {Release Year},
{track:00}, {medium:00}, {Medium Format}, {Track Title}, {Track
CleanTitle}, {Track ArtistName}, {Genre}) with Lidarr's word-separator
and case variants, colon replacement modes and replace/remove for other
illegal characters. Empty brackets and separators left by missing values
are cleaned up. Defaults to Artist/Album/01 Title with Disc 01 folders
for multi-disc albums; earlier pattern/disc settings are converted.

Examples are now rendered by the server with the same code as real
renames, fixing the settings page showing paths that differed from what
would happen (e.g. disc 1 of a multi-disc album outside its Disc folder).

"Rename now..." checks one or both libraries, then lists every change
grouped by destination folder with per-file and per-folder selection,
skipped files with reasons and a Fix tags button, and warnings; applying
re-checks each file, renames, and rescans. The pre-action backup runs
first when enabled. Migration 9 stores the naming as JSON.

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

README.md

@@ -83,16 +83,23 @@ tags** buttons. Edits are safe with hardlinks:
 - Each edit is listed in History (old → new values) and can be undone; an in-place edit interrupted by a crash is rolled back on
   startup. Dry run applies.
 
-**Organize (rename files from tags).** The *Organize* tab sets a naming layout, by default `{artist}/{album}/{track} {title}` →
-`Avenged Sevenfold/Nightmare/01 Nightmare.flac` (`{artist}` is the album artist, falling back to the artist). Tokens: `{artist}`,
-`{album}`, `{track}`, `{title}`, `{year}`, `{disc}`, `{track_artist}`, `{genre}`. Multi-disc albums get a disc prefix (`2-04 Title`) or
-a `Disc 02` folder (two-digit disc numbers by default, optionally `Disc 2`), and names are made safe for Windows/SMB shares (`AC/DC` → `AC-DC`, `Title: Sub` → `Title - Sub`).
+**Organize (rename files from tags).** The *Organize* tab sets how files are named, in the style of Lidarr: an **artist folder**, an
+**album folder**, a **track format** and a separate **multi-disc track format**, with presets. The default is
+`{Artist Name}/{Album Title}/{track:00} {Track Title}`, and multi-disc albums get `{Medium Format} {medium:00}/…` → `Disc 01`, `Disc 02`.
 
-With **Organize automatically** set to the slave, the master or both (off by default), every scan renames files that don't follow the
-layout. Files are only moved within their library, so contents and hardlinks never change; lyrics (`.lrc`) move with their song, cover
-art follows a whole folder, and emptied folders are removed. Files with missing tags or clashing names are left alone (fix their tags
-in the *Tags* tab). Each rename is in History and can be undone, and dry run applies. A slave file that is a hardlink of a master file
-at a different path is still recognised as linked.
+Tokens: `{Artist Name}`, `{Artist NameThe}` (The Beatles → Beatles, The), `{Artist CleanName}`, `{Artist NameFirstCharacter}`,
+`{Album Title}`, `{Album TitleThe}`, `{Album CleanTitle}`, `{Release Year}`, `{track:0}`/`{track:00}`, `{medium:0}`/`{medium:00}`,
+`{Medium Format}`, `{Track Title}`, `{Track CleanTitle}`, `{Track ArtistName}`, `{Genre}`. Like Lidarr, `{Artist.Name}` or `{Artist_Name}`
+puts dots or underscores between words and `{ARTIST NAME}` / `{artist name}` change the case. The artist is the album artist, falling back
+to the artist. Colons can be replaced smartly (`A: B` → `A - B`), with a dash, space dash, space dash space, or deleted; other characters
+Windows/SMB rejects are replaced (`AC/DC` → `AC-DC`) or removed. Brackets and separators left empty by a missing value are cleaned up
+(`Album ({Release Year})` without a year → `Album`). Examples are rendered by the same code that renames files.
+
+**Rename now…** checks the slave, the master or both, then shows every change grouped by destination folder (old → new, selectable per
+file or folder), plus skipped files with the reason and a *Fix tags* button. Files are only moved within their library, so contents and
+hardlinks never change; lyrics (`.lrc`) move with their song, cover art follows a whole folder, and emptied folders are removed. Each
+rename is in History and can be undone, and the library is rescanned afterwards. **Organize automatically** (off by default) applies the
+same renames during every scan. A slave file that is a hardlink of a master file at a different path is still recognised as linked.
 
 **Backups** (Settings → Backups), similar to Sonarr. A backup is a zip of playlink's database (settings, library pairs, scan results and
 history, not music files) taken safely while the app runs. Choose a folder (default `/config/backups`), a schedule (off, every 1, 3, 7