Improve MindSpace visual editor UX and default RMB billing.

Add color-coded edit highlights with an in-preview legend, strip CSP meta
for srcdoc editing, and simplify fullscreen preview to immersive visual edit
only. Default billing to CNY token rates unless H5_USE_BACKEND_COST=1.

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -23,6 +23,7 @@ H5_PUBLIC_BASE_URL=http://127.0.0.1:8081
 DATABASE_URL=mysql://boot:password@localhost:3306/tkmind
 # 或分别设置 MYSQL_HOST / MYSQL_PORT / MYSQL_USER / MYSQL_PASSWORD / MYSQL_DATABASE
 H5_USERS_ROOT=/root/tkmind_go/users
+# 新用户赠送余额（人民币分，500 = ¥5.00；勿与美元 cents 混淆）
 H5_SIGNUP_BALANCE_CENTS=500
 H5_ADMIN_USERNAME=admin
 H5_ADMIN_PASSWORD=change-me-admin
@@ -47,12 +48,13 @@ H5_ADMIN_PASSWORD=change-me-admin
 # H5_LOCAL_LLM_NAME=Local Ollama 7B
 H5_ACCESS_PASSWORD=change-me
 
-# 计费（Phase 2）
-# H5_USE_BACKEND_COST=1        # 优先用后端 accumulatedCost（USD）计费
-# H5_USD_CNY_RATE=7.2
-# H5_BILL_INPUT_CENTS_PER_1K=2
-# H5_BILL_OUTPUT_CENTS_PER_1K=6
+# 计费（Phase 2，金额单位均为人民币分）
+# 默认按 Token 单价扣费（人民币结算）；勿开启美元成本换算除非明确需要
+# H5_USE_BACKEND_COST=0
+# H5_BILL_INPUT_CENTS_PER_1K=2   # 输入 Token：2 分/1k（¥0.02/1k）
+# H5_BILL_OUTPUT_CENTS_PER_1K=6  # 输出 Token：6 分/1k（¥0.06/1k）
 # H5_MIN_BILL_CENTS=1
+# 仅调试：H5_USE_BACKEND_COST=1 + H5_USD_CNY_RATE=7.2（上游 USD × 汇率 → 人民币分）
 
 # 用户自助充值（微信支付）
 # H5_RECHARGE_TIERS_CENTS=500,1000,3000,5000,10000,20000