fix: narrow variables Tutor topic activation

[ttbombadil]

Summary

• remove bare type-used:int activation from variables-and-serial
• retain activation on the detectable serial-call: print fact
• replace the ambiguous Integer-variable question with generic Integer-datatype wording
• update the exact SHA-256 pin

Validation against UnoSim main a2254bc67e6df13ab8273923b07abbad660d1a5c

• CourseContentLoader: 35 Examples, Examples valid, Tutor valid
• Topics and Strategies parse successfully
• all four SHA-256 values pass
• PWM sketch: no variables-and-serial match
• serial Example: variables-and-serial match
• annotations remain stripped from loaded Example source

No Example source, Revision B, or UnoSim changes.

[ttbombadil]

Tutor Quality Stage 1 is now available for review in #3 and supersedes the implementation scope of this PR. The narrowed variables-and-serial activation from #2 is retained and covered by the Stage 1 content-quality gate. This PR remains open intentionally; no automatic close or merge was performed.