Add GET /oil-prices/county/:county_id public endpoint to serve scraped
oil price data by county. Includes oil_prices table definition in schema
and a backfill script to populate county_id on existing records.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Migrated JWT authentication from localStorage to httpOnly cookies using axum-extra. Refactored vendor listing and edit pages to use the centralized API client. Updated schema and data models to support these changes.
