docs(tcc): recalibrate guided activity helpTexts — instigate without spoiling

Remove explanatory passages that were answering the questions inside the
help text itself (latency/throughput distinction, RAW explanation, nop
causality, AMAT trade-off commentary, thrashing definition, 5× limit
reveal, list of CPI-reduction phenomena).

Each helpText now contains only:
- operational steps (which preset, where to look, what field to read)
- a minimal term definition where the student would otherwise be blocked
  by an unknown acronym (CPI, AMAT, LRU, FIFO)
- an open question that frames attention without framing the answer

Author: Gaok1