docs: 0.2.6.3 — what was measured, the manual, and Sunday's checks

Why black and white is made with Ghostscript and how close it is to what
Elmer prints; why Print image goes through the engine's copy image, with
the table of what each other way failed on; what it cannot reach (a CSS
background picture) and what it costs (the clipboard lives in Wonder Ink
afterwards). The manual says Print page and Print image, and that the
preview turns grey. Sunday's paper checks for both, in testing.md.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/backlog.md

@@ -1,9 +1,10 @@
 # Backlog — 0.3.0 and later
 
 Recorded after hands-on testing of 0.2.6.1 in September 2026. **None of
-this is in 0.2.6.2**, which is limited to picture printing, the
-Presentations memory failure and the settings lockdown. Each item says
-what was observed, so whoever picks it up starts from the evidence.
+this is in 0.2.6.2 or 0.2.6.3**: 0.2.6.2 is limited to picture printing,
+the Presentations memory failure and the settings lockdown, and 0.2.6.3
+to the black-and-white preview and Print image. Each item says what was
+observed, so whoever picks it up starts from the evidence.
 
 ## Wonder Ink
 
@@ -23,6 +24,15 @@ what was observed, so whoever picks it up starts from the evidence.
 - **Readable worksheet names.** Tabs show the downloaded file's name,
   which for many worksheets is a long generated prefix. Strip it, or take
   the name from the PDF's own title.
+- **Print image and CSS background pictures** (from 0.2.6.3). The engine's
+  hit test does not call a CSS background a picture, so right-click there
+  offers only Print page. Only worth doing if Sunday's testing finds
+  Wonder Ink's site draws artwork that way; the lab has no account to
+  tell. See wonder-ink.md, *Print image*.
+- **The clipboard after Print image** (from 0.2.6.3). It is put back, but
+  owned by Wonder Ink afterwards, so text copied elsewhere before is gone
+  once Wonder Ink closes — there is no clipboard manager in the session.
+  Measured, and judged smaller than leaving the picture there.
 - **A speaker on the tab that is playing sound** (`QWebEnginePage.recentlyAudible`).
 - **Linked lesson text opens an intermediate popup** instead of following
   the link, where Chrome follows it directly. Investigate: probably a