fix(runtime): honor process environment during startup

[H-TTTTT]

Summary

• validate installed startup configuration from both an optional .env file and process.env
• preserve runtime precedence by letting process environment values override file values
• allow non-interactive and daemon startup without creating an .env file when required variables are already supplied
• document process environment support and precedence

Testing

• npm run lint
• npm run build
• BOT_LOCALE=en npm test (122 files, 1100 tests)
• BOT_LOCALE=zh npm test -- tests/runtime/bootstrap.test.ts

Closes #154