chore(config,admin,api): Update default accent color to white and add PORT environment variable

- Change default accent color from #00D4AA (teal) to #FFFFFF (white) across all components
- Update AccentColorContext default state to use white accent color
- Update admin page form defaults and placeholders to reflect new accent color
- Update node API endpoint default accent color response
- Add optional PORT environment variable configuration to .env.example with default value of 3000
- Standardize branding color scheme for consistency across the application

.env.example

@@ -3,6 +3,9 @@
 # ===========================================
 # Copy this file to .env and fill in your values
 
+# Server Port (Optional, defaults to 3000)
+# PORT=3000
+
 # Database (Required)
 DATABASE_URL=postgresql://user:password@localhost:5432/synapsis