[Feature Request] /insights date range filter (--since flag)

\/insights\ analyzes all sessions in \~/.claude/usage-data/\ with no way to limit the time window. As the data accumulates, older findings become stale — issues that have already been addressed keep appearing in friction analysis and suggestions.

Request

Add a \--since\ argument to \/insights\ to filter sessions by recency.

Example usage:
\\\
/insights --since 30d # last 30 days
/insights --since 2w # last 2 weeks
/insights --since 2026-07-01 # since a specific date
\\\

Why it's straightforward to implement

Each \session-meta/*.json\ file already has a \start_time\ field (ISO 8601), so date filtering is a simple pre-pass before analysis. The \facets/*.json\ files can be matched by \session_id\.

Current workaround

Manually archiving older files before running \/insights\, which is tedious and error-prone.