fix: Remove hardcoded ports, support custom port configuration

- Replace all hardcoded localhost:8000/3000/8501 with environment variables
- Frontend: Use API_PORT env var in next.config.ts
- Backend: Use API_PORT env var in editor.py and quality.py
- Web UI: Use API_PORT and EDITOR_PORT env vars in all Streamlit pages
- Update dev.sh to pass environment variables to all services
- Add .env.example with port configuration template

Now supports custom ports via environment variables:
  API_PORT=8080 EDITOR_PORT=3001 WEB_PORT=8502 ./dev.sh

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web/pages/3_📋_Tasks.py

@@ -22,6 +22,7 @@ Features:
 import streamlit as st
 import requests
 import time
+import os
 from datetime import datetime
 
 from web.i18n import tr, get_language
@@ -33,8 +34,12 @@ st.set_page_config(
     layout="wide",
 )
 
+# Get ports from environment
+API_PORT = os.getenv("API_PORT", "8000")
+EDITOR_PORT = os.getenv("EDITOR_PORT", "3000")
+
 # API endpoint
-API_BASE = "http://localhost:8000/api"
+API_BASE = f"http://localhost:{API_PORT}/api"
 
 
 def get_all_tasks():
@@ -183,7 +188,7 @@ def render_task_card(task):
             with col_a:
                 st.success("✨ 视频生成成功")
             with col_b:
-                editor_url = f"http://localhost:3000/editor?storyboard_id={task_id}"
+                editor_url = f"http://localhost:{EDITOR_PORT}/editor?storyboard_id={task_id}"
                 st.markdown(
                     f'''
                     <a href="{editor_url}" target="_blank" style="text-decoration: none;">