[Feature]: Export analytics data to CSV

[fuleinist]

Component

Analytics (new metrics / charts)

Problem or Use Case

Users viewing their analytics dashboard may want to export session metrics, token usage, and cost data for further analysis in spreadsheets or reporting tools. Currently, this data is only viewable within the dashboard.

Proposed Solution

Add an "Export to CSV" button on the Analytics page that downloads a CSV file containing the filtered analytics data (sessions, tokens, costs, cache hit rates, model distribution for the selected time period).

Use Case

I track my AI usage costs across multiple tools and need to consolidate data in a spreadsheet for monthly reporting. Being able to export Claude Code Karma analytics would make this much easier.

Alternatives Considered

• JSON export (more structured but less universally usable)
• Copy-paste from the UI (error-prone)

Additional Context

The analytics endpoint already has the data structured; this would primarily need a CSV serialization step and a download trigger in the frontend.