raw derive PDF: Kopf nennt Bildseiten (images) und nicht zugeordnete Seiten (unmatched); neue Anweisung read-page-images für den gezielten Blick auf diese Seiten, Schwelle 20 Seiten (#234); 10.1.0-beta.7

Files changed:
- CHANGES.md
- VERSION
- docs/how-to/ingest-a-source.md
- docs/reference/commands/raw-material-and-uploads.md
- instructions/ingest-large-tree.md
- instructions/read-page-images.md
- instructions/wiki-ingest/SKILL.md
- raw/CONTRACT.md
- tools/CONTRACT.md
- tools/chemenu/commands/raw/derive.py
- tools/chemenu/filters/pdf.py
- tools/chemenu/filters/pdf_layout.py
- tools/chemenu/tests/test_raw_derive_binary.py
- types/source.guidance.md

Co-Authored-By: Claude Code <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

raw/CONTRACT.md

@@ -410,8 +410,11 @@ whitespace and never crosses a line or a page marker. A page whose text cannot b
 layout gets no markings and a WARN. A CHECK names the pages whose pictures the text does not
 hold, because the tool has no OCR: a picture counts unless it is a background covering most of
 the page, a filler a few pixels or points in size, or the same picture on a fifth of the pages
-(a logo, a frame); a vector drawing with many paths and little text counts too. A PDF without
-outline or markings is derived as before. Reading the layout needs `pdfminer.six` beside
+(a logo, a frame); a vector drawing with many paths and little text counts too. The same pages
+stand in the header, so they outlast the output: `images` for the CHECK's pages, `unmatched` for
+the pages of that WARN, each a page range and each only when not empty. What an ingest does with
+them is [read-page-images.md](../instructions/read-page-images.md). A PDF without outline,
+markings, images and unmatched pages is derived as before. Reading the layout needs `pdfminer.six` beside
 `pypdf`.
 
 **The original stays.** The derivation is the tool's reading of it, never the source: with the