chore: change local development port from 8000 to 8100

- Update docker-compose.yml to map host port 8100 -> container 8000
- Update all Playwright test BASE_URL to port 8100
- Update .env.example with documentation about port mapping
- This avoids conflicts with other services on port 8000

docker-compose.yml

@@ -5,7 +5,7 @@ services:
       dockerfile: Dockerfile
     image: vault-dash:dev
     ports:
-      - "8000:8000"
+      - "8100:8000"
     environment:
       APP_ENV: development
       APP_HOST: 0.0.0.0