feat(kernel): ✨ Add typed environment schema

[haskou]

Summary

• Adds typed environment schemas for Kernel so applications can declare expected variables, types and required/default values.
• Parses string, number and boolean environment values after loading dotenv files.
• Throws KernelEnvironmentValidationError when required variables are missing or values cannot be parsed.
• Updates the example and docs to use kernel.environment with inferred types.

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

[chatgpt-codex-connector]

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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