fix(media): a tag-scan placeholder is not a book identity

The first real plan filed 1,106 chapters from 14 unrelated top-level folders
onto one shelf, because all 1,106 carry the album tag [Unknown Album] and the
same artist tag. Plex's album title is the authority for the shelf only when it
names a book; a placeholder names nothing, and unrelated books share it. Those
chapters now park with the path they have today, timestamp-glued variants
included; Various Artists stays a legitimate multi-cast narrator.

serverAppConfigs-docs/Dankserver/Media Relayout.md

@@ -336,8 +336,7 @@ The group is the identity Plex asserts in its own database — **(narrator, book
 year)** — so one book arriving in four part folders becomes one folder, and a
 1965 and a 2020 recording that share a title stay two books.
 
-Two laws here are the opposite of the music arm's, and both are forced by what
-the rows actually hold:
+Two laws are forced by what the rows actually hold:
 
 +- **A chapter is never renumbered.** Most books contain chapters whose index Plex
   does not know, so a number written into a name would be invented — and it would
@@ -352,8 +351,10 @@ the rows actually hold:
 
 What it refuses, the music arm's list with one addition: a video container, audio
 no chapter row names, and a loose file in a folder holding two books all park under
-`_unsorted` with the path they have today — and so does a chapter whose row has
-**no book or no narrator**, because inventing a shelf is filing it wrong.
+`_unsorted` with the path they have today — and so does a chapter whose row names
+**no book or no narrator**, placeholder included (`[Unknown Album]`, `no title`,
+`[Unknown Artist]`): unrelated books share those strings, so filing on one merges
+them. `Various Artists` is not a placeholder — that is a multi-cast read.
 
 ## Laws