Verify Ben-Ari (1998) full text: 'no effective model of a computer'

[dbosk]

`literature/mental-models.bib` (entry `BenAri1998Constructivism`) is flagged TODO: only the abstract of Constructivism in computer science education (SIGCSE 1998, DOI 10.1145/273133.274308) could be verified in-session; the ACM PDF was inaccessible.

To do (manual, library access):

• Retrieve the full text (ACM DL, should be accessible from KTH).
• Verify whether/where the famous claim that a beginning student "has no effective model of a computer" appears, and extract the verbatim quote.
• Update the QUOTE and VERIFIED fields of the provenance block in `literature/mental-models.bib`.

This claim is central support for the hardware/OS/kernel/shell deconstruction intro (evaluation/improvements.md, theme 4) — do not attribute it before this check.