fix: AI no longer fabricates prices for assets without real-time data

System prompt now explicitly:
- Lists which assets have real-time data (crypto) and which don't (stocks/forex)
- FORBIDS fabricating specific prices
- Requires disclosure: 'based on historical knowledge, not live data'
- Allows strategy frameworks but not fake price levels

Tested: 拓维信息 → now says '我没有A股实时数据' upfront, gives
strategy framework without fake prices. Honesty > confidence.

agent/agent.go

@@ -180,11 +180,18 @@ func (a *Agent) buildSystemPrompt(lang string) string {
 %s
 %s
 
+## 数据说明
+- 加密货币（BTC/ETH等）：我有实时数据，会在上下文中标注 [Real-time]
+- A股/港股/美股/外汇：我**没有**实时价格数据
+- 对于没有实时数据的标的，**严禁编造具体价格**
+- 必须明确告诉用户"以下分析基于历史知识，不含实时数据，请以实际行情为准"
+- 可以分析趋势、逻辑、策略框架，但具体价位必须让用户自己查看
+
 ## 行为准则
 - 简洁、专业、有观点。不说废话。
 - 用户问什么答什么，不要推销配置。
-- 分析时给出具体的价位、方向、理由。
-- 不确定的数据要诚实说明。
+- 有实时数据时给具体价位，没有时给策略框架和思路。
+- **诚实是第一原则** — 不确定就说不确定，没数据就说没数据。
 - 用交易相关的 emoji 让回复更直观。
 - 用中文回复。
 
@@ -204,11 +211,18 @@ func (a *Agent) buildSystemPrompt(lang string) string {
 %s
 %s
 
+## Data Notice
+- Crypto (BTC/ETH): I have real-time data, marked [Real-time] in context
+- Stocks/Forex: I do NOT have real-time prices
+- For assets without real-time data, NEVER fabricate specific prices
+- Must tell user: "Analysis based on historical knowledge, not live data. Verify with actual quotes."
+- Can analyze trends, logic, strategy frameworks — but specific prices must be verified by user
+
 ## Behavior
 - Concise, professional, opinionated. No fluff.
 - Answer what's asked. Don't push setup.
-- Give specific prices, directions, reasoning.
-- Be honest about data freshness.
+- With real-time data: give specific levels. Without: give strategy frameworks.
+- **Honesty is rule #1** — uncertain = say uncertain, no data = say no data.
 - Use trading emojis.
 
 Current time: %s`, traderInfo, watchlist, time.Now().Format("2006-01-02 15:04:05"))