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>

console/screens/admin_crossref.py

@@ -1,5 +1,5 @@
 """
-Admin CRUD screen for Cross-References in the AUTOPARTES console application.
+Admin CRUD screen for Cross-References in the NEXUS AUTOPARTS console application.
 
 Provides a paginated list view with create (F3), edit (ENTER), and
 delete (F8/Del) operations for the part_cross_references table.

console/screens/admin_fabricantes.py

@@ -1,5 +1,5 @@
 """
-Admin CRUD screen for Manufacturers in the AUTOPARTES console application.
+Admin CRUD screen for Manufacturers in the NEXUS AUTOPARTS console application.
 
 Provides a list view with create (F3), edit (ENTER), and delete (F8/Del)
 operations for the manufacturers table.

console/screens/admin_import.py

@@ -1,5 +1,5 @@
 """
-Import/Export screen for the AUTOPARTES console application.
+Import/Export screen for the NEXUS AUTOPARTS console application.
 
 Provides a simple menu flow to import CSV files into the database or
 export data to JSON files.  Uses the renderer's show_input and

console/screens/admin_partes.py

@@ -1,5 +1,5 @@
 """
-Admin CRUD screen for Parts in the AUTOPARTES console application.
+Admin CRUD screen for Parts in the NEXUS AUTOPARTS console application.
 
 Provides a paginated list view with create (F3), edit (ENTER), and
 delete (F8/Del) operations.  Form editing is handled inline with

console/screens/buscar_parte.py

@@ -1,5 +1,5 @@
 """
-Part number search screen for the AUTOPARTES console application.
+Part number search screen for the NEXUS AUTOPARTS console application.
 
 Prompts the user for a part number (OEM, aftermarket, or cross-reference)
 and displays matching results in a table.  Selecting a result navigates

console/screens/buscar_texto.py

@@ -1,5 +1,5 @@
 """
-Full-text search screen for the AUTOPARTES console application.
+Full-text search screen for the NEXUS AUTOPARTS console application.
 
 Prompts the user for a search query and displays matching parts using
 the FTS5 full-text search engine (with LIKE fallback).  Results are

console/screens/catalogo.py

@@ -1,5 +1,5 @@
 """
-Catalog navigation screen for the AUTOPARTES console application.
+Catalog navigation screen for the NEXUS AUTOPARTS console application.
 
 Provides a three-level drill-down through the parts hierarchy:
 Categories -> Groups -> Parts.  An optional vehicle filter (mye_id)

console/screens/comparador.py

@@ -1,5 +1,5 @@
 """
-Part comparator screen for the AUTOPARTES console application.
+Part comparator screen for the NEXUS AUTOPARTS console application.
 
 Displays a side-by-side comparison of an OEM part against its aftermarket
 alternatives.  The first column is always the OEM part; subsequent columns

console/screens/estadisticas.py

@@ -1,5 +1,5 @@
 """
-Statistics dashboard screen for the AUTOPARTES console application.
+Statistics dashboard screen for the NEXUS AUTOPARTS console application.
 
 Displays database table counts and coverage metrics retrieved via
 :meth:`Database.get_stats`.

console/screens/menu_principal.py

@@ -1,5 +1,5 @@
 """
-Main menu screen for the AUTOPARTES console application.
+Main menu screen for the NEXUS AUTOPARTS console application.
 
 Displays a numbered Pick-style menu with navigation options for all
 application sections.  Number keys jump directly; arrow keys move the

console/screens/parte_detalle.py

@@ -1,5 +1,5 @@
 """
-Part detail screen for the AUTOPARTES console application.
+Part detail screen for the NEXUS AUTOPARTS console application.
 
 Shows full part information (OEM number, name, group, category, etc.)
 with a table of aftermarket alternatives.  Number keys navigate to

console/screens/vehiculo_nav.py

@@ -1,5 +1,5 @@
 """
-Vehicle drill-down navigation screen for the AUTOPARTES console application.
+Vehicle drill-down navigation screen for the NEXUS AUTOPARTS console application.
 
 Guides the user through a four-level hierarchy:
 

console/screens/vin_decoder.py

@@ -1,5 +1,5 @@
 """
-VIN decoder screen for the AUTOPARTES console application.
+VIN decoder screen for the NEXUS AUTOPARTS console application.
 
 Prompts for a 17-character Vehicle Identification Number, decodes it
 via the NHTSA vPIC API (with local caching), and displays the decoded