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>

dev.sh

@@ -54,7 +54,7 @@ print_banner() {
 
 start_api() {
     echo -e "${GREEN}🚀 Starting FastAPI Backend...${NC}"
-    uv run python api/app.py --port $API_PORT --reload &
+    API_PORT=$API_PORT uv run python api/app.py --port $API_PORT --reload &
     echo $! > "$PID_DIR/api.pid"
     echo -e "   ${GREEN}✓${NC} API running at: ${YELLOW}http://localhost:$API_PORT${NC}"
     echo -e "   ${GREEN}✓${NC} API Docs at: ${YELLOW}http://localhost:$API_PORT/docs${NC}"
@@ -63,7 +63,7 @@ start_api() {
 start_editor() {
     echo -e "${GREEN}🎬 Starting Next.js Editor...${NC}"
     cd "$PROJECT_ROOT/frontend"
-    PORT=$EDITOR_PORT npm run dev &
+    API_PORT=$API_PORT PORT=$EDITOR_PORT npm run dev &
     echo $! > "$PID_DIR/editor.pid"
     cd "$PROJECT_ROOT"
     echo -e "   ${GREEN}✓${NC} Editor running at: ${YELLOW}http://localhost:$EDITOR_PORT${NC}"
@@ -71,7 +71,7 @@ start_editor() {
 
 start_web() {
     echo -e "${GREEN}🌐 Starting Streamlit Web UI...${NC}"
-    uv run streamlit run web/app.py --server.port $WEB_PORT &
+    API_PORT=$API_PORT EDITOR_PORT=$EDITOR_PORT uv run streamlit run web/app.py --server.port $WEB_PORT &
     echo $! > "$PID_DIR/web.pid"
     echo -e "   ${GREEN}✓${NC} Web UI running at: ${YELLOW}http://localhost:$WEB_PORT${NC}"
 }