feat: migrate to PostgreSQL + SQLAlchemy ORM, rebrand to Nexus Autoparts

- Migrate from SQLite to PostgreSQL with normalized schema
- Add 11 lookup tables (fuel_type, body_type, drivetrain, transmission,
  materials, position_part, manufacture_type, quality_tier, countries,
  reference_type, shapes)
- Rewrite dashboard/server.py (76 routes) using SQLAlchemy text() queries
- Rewrite console/db.py (27 methods) using SQLAlchemy ORM
- Add models.py with 27 SQLAlchemy model definitions
- Add config.py for centralized DB_URL configuration
- Add migrate_to_postgres.py migration script
- Add docs/METABASE_GUIDE.md with complete data entry guide
- Rebrand from "AUTOPARTS DB" to "NEXUS AUTOPARTS"
- Fill vehicle data gaps via NHTSA API + heuristics:
  engines (cylinders, power, torque), brands (country, founded_year),
  models (body_type, production years), MYE (drivetrain, transmission, trim)

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

dashboard/enhanced-search.js

@@ -10,7 +10,7 @@ const enhancedSearch = {
         debounceMs: 300,
         maxResults: 8,
         maxRecent: 5,
-        storageKey: 'autopartes_recent_searches'
+        storageKey: 'nexus_recent_searches'
     },
 
     // State