feat: add optional cwd path argument to serve command

[pschiel]

Problem:

• for debugging, bun needs to start in the development build directory
• makes it currently impossible to debug different scenarios/projects

This patch adds positional argument for cwd folder opencode serve [cwd]

Usage:

bun run --cwd ${OPENCODE_DEV_PATH} --inspect-wait=ws://localhost:6499/ ./src/index.ts \
  serve --port 4096 /my/project/path