feat(kernel): ✨ Add environment variable loader

[haskou]

Summary

• Adds kernel.loadEnvironmentVariables(environment?) and Kernel.loadEnvironmentVariables(environment?) backed by dotenv.
• Adds kernel.environment and Kernel.environment as typed access points over process.env.
• Documents environment loading, typed NodeJS.ProcessEnv augmentation and startup usage.
• Updates the example to load environment variables before DI and adapter setup.

Validation

• yarn format:check
• yarn lint
• yarn typecheck
• yarn test:coverage (100%)
• yarn docs:build
• yarn build
• yarn --cwd example typecheck
• npx -y depcheck --json

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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