♻️ Rewrite impression share CLI for search term data

Impression share reports return search term data (not keyword data),
so the CLI has been rewritten to work with the actual API response.

Commands:
- analyze: Show search term impression share with filtering
- report: Generate detailed report with CSV export
- summary: Country-level aggregated statistics

Removed the optimize command as search terms cannot be directly mapped
to keywords for bid adjustments (search terms can match multiple keywords).

Author: SamPetherbridge