recordPromptUsage method
Record that a prompt suggestion was used (for ranking).
Implementation
void recordPromptUsage(String promptText) {
final idx = _promptSuggestions.indexWhere((s) => s.text == promptText);
if (idx >= 0) {
_promptSuggestions[idx] = _promptSuggestions[idx].copyWith(
usageCount: _promptSuggestions[idx].usageCount + 1,
lastUsed: DateTime.now(),
);
}
}