refactor(environment): update virtualenv path to /opt/venv in Docker setup

- Adjusted `docker-compose.dev.yml` to reflect the new venv location.
- Modified entrypoint script and Dockerfile to reference `/opt/venv` for isolated dependencies.
- Improved bind mount setup to prevent venv overwrites during development.

docker-compose.dev.yml

@@ -40,8 +40,7 @@ services:
     volumes:
       - ./backend:/app
       - ./uploads:/app/uploads
-      # Exclude local .venv from bind mount to use container's .venv
-      - /app/.venv
+      # Note: venv is at /opt/venv (not /app/.venv) so bind mount doesn't affect it
     ports:
       - "8000:8000"
     env_file:
@@ -76,7 +75,6 @@ services:
       target: development
     volumes:
       - ./backend:/app
-      - /app/.venv
     env_file:
       - .env
     environment:
@@ -99,7 +97,6 @@ services:
       target: development
     volumes:
       - ./backend:/app
-      - /app/.venv
     env_file:
       - .env
     environment:
@@ -122,7 +119,6 @@ services:
       target: development
     volumes:
       - ./backend:/app
-      - /app/.venv
     env_file:
       - .env
     environment:
@@ -145,7 +141,6 @@ services:
       target: development
     volumes:
       - ./backend:/app
-      - /app/.venv
     env_file:
       - .env
     environment: