FLX-8030: generated evidence prose contains a reserved word

Family: evidence/pack (the 8000 band)

EVIDENCE.md is rendered from a fixed template, but a caller-supplied value (a bundle name, a conformance summary) can still introduce a word this project reserves (the list is in flux_engine/_vocabulary.py). The report is refused rather than written with the word inside it.

Look it up offline

$ fluxsim explain FLX-8030

Every code is listed in the error index.