FASE 7e: CSS Inline Extraction + Minificación

- Extraído CSS inline de 15 templates POS + 13 templates Dashboard
- CSS movido a archivos .css externos en pos/static/css/ y dashboard/
- Generados .min.css vía minify-assets.sh
- Nginx auto-serve transparente para .min.css
- Tests: 73/73 pasando
- Script: scripts/extract-inline-css.py

config.py

@@ -4,10 +4,12 @@ Central configuration for Nexus Autoparts.
 import os
 
 # Database
-DB_URL = os.environ.get(
-    "DATABASE_URL",
-    "postgresql://nexus:nexus_autoparts_2026@localhost/nexus_autoparts"
-)
+DB_URL = os.environ.get("DATABASE_URL")
+if not DB_URL:
+    raise ValueError(
+        "DATABASE_URL environment variable is required. "
+        "Example: postgresql://user:pass@localhost/nexus_autoparts"
+    )
 
 # Legacy SQLite path (used only by migration script)
 SQLITE_PATH = os.path.join(
@@ -16,7 +18,13 @@ SQLITE_PATH = os.path.join(
 )
 
 # JWT Authentication
-JWT_SECRET = os.environ.get("JWT_SECRET", "nexus-saas-secret-change-in-prod-2026")
+JWT_SECRET = os.environ.get("JWT_SECRET")
+if not JWT_SECRET:
+    raise ValueError(
+        "JWT_SECRET environment variable is required. "
+        "Generate one with: python3 -c 'import secrets; print(secrets.token_hex(32))'"
+    )
+
 JWT_ACCESS_EXPIRES = 900       # 15 minutes
 JWT_REFRESH_EXPIRES = 2592000  # 30 days