Add Oxlint configuration and integrate linting commands

- Introduced a new `.oxlintrc.json` file to configure Oxlint for code quality checks.
- Updated `package.json` to include linting scripts (`lint` and `lint:fix`) for easier code maintenance.
- Enhanced documentation in `README` files to guide users on running Oxlint checks and applying fixes.

src/strategy/swing-engine.ts

@@ -422,7 +422,7 @@ export class SwingEngine {
         : position.entryPrice * (1 + Math.max(0, this.config.stopLossPct));
 
     const tick = Math.max(1e-9, this.config.priceTick);
-    const lastPrice = referencePrice ?? Number(this.tickerSnapshot?.lastPrice) ?? null;
+    const lastPrice = referencePrice;
 
     // Kill-switch (always-on).
     const triggerKill =
@@ -621,4 +621,3 @@ export class SwingEngine {
       });
   }
 }
-