docs: add technical description for Ping-Pong strategy with RSI and Hurst Bands

STRATEGY_PING_PONG.md

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+# Ping-Pong Trading Strategy (RSI & Hurst Bands)
+
+The Ping-Pong strategy is an **accumulation and volatility harvesting system** designed for range-bound or trending markets. It utilizes a series of "pings" (small trades) to build a position during dips (Long) or peaks (Short) and takes profits incrementally during price reversals.
+
+## 1. Core Indicators
+
+### A. RSI (Relative Strength Index)
+- **Calculation**: Standard 14-period RSI using Rolling Moving Average (RMA) smoothing.
+- **Overbought/Oversold**: Default levels are **70/30**.
+- **Crossover Logic (Long Mode)**:
+    - **Accumulate (BUY)**: RSI crosses **UP** through the `oversold` level (e.g., from 29 to 31).
+    - **Partial Exit (SELL)**: RSI crosses **DOWN** through the `overbought` level (e.g., from 71 to 69).
+
+### B. Hurst Bands
+- **Structure**:
+    - **Center Line**: A Rolling Moving Average (RMA) shifted backward by half the period to center it on price action.
+    - **Bands**: Center Line ± (Multiplier * ATR).
+- **Crossover Logic (Long Mode)**:
+    - **Accumulate (BUY)**: Price (Close) crosses **DOWN** below the `hurst_lower` band.
+    - **Partial Exit (SELL)**: Price (Close) crosses **UP** above the `hurst_upper` band.
+
+---
+
+## 2. Execution Logic (Long Direction)
+
+The strategy operates on a **Crossover-only** trigger mechanism on every new candle.
+
+### A. Opening & Accumulation (`Signal: OPEN`)
+Triggered if **EITHER** RSI or Hurst generates a BUY signal (and both are enabled).
+- **Trade Size**: `pos_size_margin * exchange_leverage` (USD).
+- **Risk Filter**: A trade is only executed if the resulting **Total Effective Leverage** (Total Position Notional / Account Equity) is less than or equal to `max_effective_leverage`.
+- **Order Type**: Market Order.
+
+### B. Closing & Partial Exit (`Signal: CLOSE`)
+Triggered if **EITHER** RSI or Hurst generates a SELL signal (and both are enabled).
+- **Exit Size**: `current_position_size * partial_exit_pct` (Default: 15%).
+- **Minimum Value Rule**: If the remaining position value after the partial exit would fall below `min_position_value_usd` (Default: $15), the **ENTIRE** position is closed.
+- **Order Type**: Market Order (with `reduceOnly=True`).
+
+---
+
+## 3. Server-Side Execution Workflow
+
+1.  **Polling**: The script polls the database every 5-10 seconds for the most recent candle data.
+2.  **Candle Detection**: When a new candle timestamp is detected, the indicator engine recalculates RSI and Hurst Bands.
+3.  **Signal Check**: The script compares the `latest` candle values with the `previous` candle values to identify strict crossovers.
+4.  **Exchange Sync**: Before execution, the script fetches the current account balance and active position from the exchange (e.g., Bybit).
+5.  **Order Placement**: Based on the calculated quantity and risk filters, it sends a Market Order to the exchange.
+
+---
+
+## 4. Key Configuration Parameters
+
+| Parameter | Type | Default | Description |
+| :--- | :--- | :--- | :--- |
+| `symbol` | string | BTCUSDT | Trading pair. |
+| `direction` | string | long | Strategy direction ("long" or "short"). |
+| `pos_size_margin` | float | 20.0 | The base USD amount for each trade (Ping). |
+| `exchange_leverage` | float | 3.0 | Multiplier for the individual trade size. |
+| `max_eff_leverage` | float | 1.0 | Hard cap on total account exposure. |
+| `partial_exit_pct` | float | 0.15 | Fraction of the position to close on a sell signal. |
+| `min_pos_val_usd` | float | 15.0 | Minimum USD value to keep a position active. |
+| `rsi_enabled` | boolean | true | Enable RSI as a trigger. |
+| `hurst_enabled` | boolean | true | Enable Hurst Bands as a trigger. |