docs: 📝 Clarify contracts and adapters

[haskou]

Summary

• Adds a package map explaining core, contracts/domain primitives and optional adapters.
• Reworks installation by adapter group instead of listing random packages without context.
• Reorganizes VitePress reference navigation by Kernel, Contracts/Domain, Pub/Sub, DB, UI, Scheduling, Logs and WebSocket.
• Expands Kernel, DependencyInjection, ConsoleKernelLogger, Route and adapters docs with clearer responsibilities and options.

Validation

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

[chatgpt-codex-connector]

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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