Feature request: Date range filtering for /insights command

Summary

Add the ability to filter /insights reports by date range.

Current Behavior

The /insights command generates a report covering all available session data. Attempts to filter by date using arguments like --days 7, from 2026-02-10, or natural language like "but only for the last week" do not affect the date range - all produce the same output.

Requested Behavior

Support date filtering options such as:

• --days N - last N days
• --from YYYY-MM-DD - sessions from a specific start date
• --to YYYY-MM-DD - sessions up to a specific end date
• --from YYYY-MM-DD --to YYYY-MM-DD - specific date range

Use Case

When reviewing usage patterns, it's useful to focus on recent activity (e.g., "what did I work on this week?") rather than the full history. This is especially relevant for:

• Weekly retrospectives
• Sprint reviews
• Comparing productivity across different time periods

Additional Context

The --help flag also doesn't display available options - it just runs another insights report.