Add organizing files into Artist/Album/01 Title from their tags

A new Organize tab renames audio files from their tags into a per-pair
naming pattern, by default {artist}/{album}/{track} {title} (album
artist, falling back to artist). Multi-disc albums get a disc prefix
(2-04) or a Disc N folder; names are made safe for Windows/SMB shares.

- Preview first: every rename, files already organized, and files
  skipped with the reason (missing tags, with a button into the tag
  editor; two files resolving to the same name; an existing file).
- Applying re-checks each file against the preview, moves it within its
  library (hardlinks and contents untouched, case-only renames via a
  temporary name, completed on startup after a crash), carries .lrc
  lyrics and folder cover art along, and removes emptied folders. Each
  move is an operation that can be undone; the library is rescanned.
- Optional automatic organizing of the slave, master or both during
  scans (off by default). Dry run applies.
- Scans now recognise a slave file that is a hardlink of a master file
  at a different path as linked ("same file, other path") instead of
  unmatched.

Migration 7 adds the per-pair naming settings.

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

internal/store/store.go

@@ -121,6 +121,11 @@ var migrations = []string{
 
 	// 6: operation-specific details as JSON (e.g. which tags an edit changed).
 	`ALTER TABLE operations ADD COLUMN detail TEXT NOT NULL DEFAULT '';`,
+
+	// 7: file organizing (renaming files from their tags).
+	`ALTER TABLE pairs ADD COLUMN organize_template TEXT NOT NULL DEFAULT '';
+	ALTER TABLE pairs ADD COLUMN organize_multidisc TEXT NOT NULL DEFAULT 'prefix';
+	ALTER TABLE pairs ADD COLUMN auto_organize TEXT NOT NULL DEFAULT 'off';`,
 }
 
 // Open opens (and migrates) the database in dataDir.