feat(CRIT-010): add zone-to-county mapping and county_id to oil_prices

Add ZONE_COUNTY_MAP for all 5 scraped states (42 zone-to-county entries).
Scraper now resolves county_id at startup and assigns it to each record.
Upsert logic deduplicates by (name, state, county_id) to prevent duplicates
when multiple zones map to the same county. Also adds County model for
DB lookups and fixes Rhode Island zone count (4, not 5).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

fuel_scraper/__init__.py

@@ -0,0 +1,4 @@
+# fuel_scraper package
+from .scraper import main
+
+__all__ = ["main"]