/insights overwrites previous reports without warning and lacks date-range filtering

Problem

Running /insights overwrites ~/.claude/usage-data/report.html without any warning. If a user had a previous report (e.g., from last month), it's silently lost.

Additionally, there's no way to generate insights for a specific time period — it's always a fixed 30-day lookback.

Suggested improvements

1. Don't overwrite existing reports — either save with timestamps (e.g., report-2026-05-06.html) or warn the user and ask for confirmation before overwriting.
2. Add date-range filtering — allow something like /insights --from 2026-04-01 --to 2026-04-15 or /insights --week last to generate reports for specific periods. Weekly breakdowns would be especially useful for tracking changes in workflow patterns over time.
3. Claude should warn about the overwrite — when a user runs /insights and a previous report exists, Claude (or the command itself) should flag that the existing report will be replaced.

Context

As a heavy user, I had a report from last month that was overwritten when running /insights again. There was no indication this would happen.