Verify du Boulay et al. (1981) full text: glass box / notional machine

[dbosk]

`literature/mental-models.bib` (entry `DuBoulay1981BlackBox`) is flagged TODO: the full text of The black box inside the glass box: presenting computing concepts to novices (Int. J. Man-Machine Studies 14(3), DOI 10.1006/ijhc.1981.0309) was not accessible in-session (publisher paywalled, figshare record metadata-only).

To do (manual, library access):

• Retrieve the full text via KTH library.
• Verify the notional-machine/glass-box definition passage and extract a verbatim quote.
• Update the QUOTE and VERIFIED fields of the provenance block in `literature/mental-models.bib`.

Needed before quoting specifics in the course-intro deconstruction material (see evaluation/improvements.md, theme 4) and any vt-catalogue work.