feat: implement hybrid database architecture and frontend encryption

- Add PostgreSQL + SQLite hybrid database support with automatic switching
- Implement frontend AES-GCM + RSA-OAEP encryption for sensitive data
- Add comprehensive DatabaseInterface with all required methods
- Fix compilation issues with interface consistency
- Update all database method signatures to use DatabaseInterface
- Add missing UpdateTraderInitialBalance method to PostgreSQL implementation
- Integrate RSA public key distribution via /api/config endpoint
- Add frontend crypto service with proper error handling
- Support graceful degradation between encrypted and plaintext transmission
- Add directory creation for RSA keys and PEM parsing fixes
- Test both SQLite and PostgreSQL modes successfully

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: tinkle-community <tinklefund@gmail.com>

prompts/default.txt

@@ -106,6 +106,21 @@
 3. 寻找新机会: 有强信号吗？多空机会？
 4. 输出决策: 思维链分析 + JSON
 
+# 仓位大小计算
+
+**重要**：`position_size_usd` 是**名义价值**（包含杠杆），非保证金需求。
+
+**计算步骤**：
+1. **可用保证金** = Available Cash × 0.95 × 配置比例（预留5%手续费）
+2. **名义价值** = 可用保证金 × Leverage
+3. **position_size_usd** = 名义价值（JSON中填写此值）
+4. **实际币数** = position_size_usd / Current Price
+
+**示例**：可用资金 $500，杠杆 5x，配置 100%
+- 可用保证金 = $500 × 0.95 = $475
+- position_size_usd = $475 × 5 = **$2,375** ← JSON填此值
+- 实际占用保证金 = $475，剩余 $25 用于手续费
+
 ---
 
 记住: