Update a specific section of the coach's memory (COACH_MEMORY.md).
Rewrites the section in-place. Call this immediately when significant
new information emerges — don't wait until session end.
Sections:
athlete — name, location, weight
prs — self-reported PRs with date assessed
goals — target race, current phase
active_flags — injuries, niggles, concerns
training_context — weekly volume, training days, constraints
patterns — observations about the athlete's training
Args:
section: Section key (athlete, prs, goals, active_flags, training_context, patterns)
content: New content for the section (replaces everything under the ## header)
Returns:
Confirmation message.