Refactor for TDD workflow with Vitest and ESLint

- Move API keys from hardcoded values to .env via dotenv
- Extract business logic into src/trading.ts with dependency injection
- Add typed AlpacaClient interface, replace `any` on Alpaca class
- Add Vitest test suites for trading logic and Alpaca wrapper (14 tests)
- Set up ESLint with @typescript-eslint for linting
- Fix getAsset to pass symbol string directly to SDK
- Fix typo (alpacha -> alpaca), remove unused ws/node-fetch deps
- Update .gitignore for node_modules and .env

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tsconfig.json

@@ -107,5 +107,6 @@
     /* Completeness */
     // "skipDefaultLibCheck": true,                      /* Skip type checking .d.ts files that are included with TypeScript. */
     "skipLibCheck": true                                 /* Skip type checking all .d.ts files. */
-  }
+  },
+  "include": ["src"]
 }