Remove the organizer's Preview and apply section

The preview/apply flow on the Organize tab did not work as expected, so
it is removed along with its backend: the stored per-pair preview, the
/organize/preview, /organize/plan and /organize/apply endpoints and
their UI and types.

The File naming card stays, and renaming now happens only through
"Organize automatically" during scans, which keeps the underlying
planning/moving code (now internal), undo, crash recovery and dry run.
The rename-folders warning is unchanged. Tests now drive the kept
planning and moving code directly.

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

README.md

@@ -83,20 +83,16 @@ 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 renames files into one 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 2` folder. 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 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 2` folder, and names are made safe for Windows/SMB shares (`AC/DC` → `AC-DC`, `Title: Sub` → `Title - Sub`).
 
-- **Preview first:** every file with its new name, what is already organized, and what is skipped and why (missing tags, with a
-  *Fix tags* button that opens the tag editor, or two files that would get the same name).
-- Files are only moved within their library, so contents and hardlinks never change. Lyrics (`.lrc`) move with their song, cover art
-  follows when a whole folder moves, and emptied folders are removed.
-- Organizing **both libraries** keeps paths in step. A slave file that is a hardlink of a master file at a different path is still
-  recognised as linked.
-- Each rename is in History and can be undone; the library is rescanned afterwards. Optionally, a pair can organize the slave, the
-  master or both automatically during every scan (off by default). Dry run applies.
+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.
 
 **Export.** The Review tab's **Export CSV** button downloads either the current view (filter and search applied) or the entire scan.
 Each row has the match status and type, a recommendation, both paths, where linking would place the file, codec, bitrate, sample rate,