perf: scan interval 50ms fixed

HL allMids pushes ~200ms, scan at 50ms catches every update
within 1 tick. Async entry goroutine means no blocking.

README.md

@@ -19,8 +19,7 @@ PriceStore ─────────┼─────────────
                     └──────────────┘
                            │
                  ┌─────────▼─────────┐
-                 │ ScanBGHL (50-250ms │
-                 │   random jitter)   │
+                 │ ScanBGHL (50ms)    │
                  │ BG ↔ HL only       │
                  └─────────┬─────────┘
                            │
@@ -98,7 +97,7 @@ Then open [http://localhost:8888](http://localhost:8888) for the Web dashboard.
 | `BITGET_API_KEY` / `BITGET_API_SECRET` / `BITGET_PASSPHRASE` | — | Bitget API credentials (test mode skips) |
 | `HL_PRIVATE_KEY` / `HL_ADDRESS` | — | HyperLiquid wallet credentials (test mode skips) |
 
-> **Note:** Scan interval is fixed at **50-250ms random jitter** (not configurable). This prevents lock-step with HyperLiquid's ~200ms push cycle.
+> **Note:** Scan interval is fixed at **50ms**. At this rate the scanner catches every HyperLiquid ~200ms push without any jitter.
 
 ## Fee Model
 
@@ -113,7 +112,7 @@ Round trip (2 legs entry + 2 legs exit): **0.07%** total fees.
 
 ## Trading Logic
 
-1. **Scanner** runs every 50-250ms (random jitter to avoid lock-step with exchange push cycles), checks all 6 coins for BG ↔ HL spread
+1. **Scanner** runs every 50ms, checks all 6 coins for BG ↔ HL spread
 2. **Entry** when net profit ≥ `TRADE_THRESHOLD` (after full round-trip fees)
    - Uses scan-time prices directly (no re-read from store to avoid WS jitter)
    - Synchronous execution in the scanner tick (no goroutine delay)