chore(frontend): migrate from npm to Bun for dependency management and scripts

- Updated README to replace npm commands with Bun equivalents.
- Added `bun.lock` file to track Bun-managed dependencies.

frontend/.gitignore

@@ -42,5 +42,5 @@ yarn-error.log*
 *.tsbuildinfo
 next-env.d.ts
 
-# Auto-generated files (regenerate with npm run generate:api)
+# Auto-generated files (regenerate with bun run generate:api)
 /src/mocks/handlers/generated.ts