docs: sync markdown with DDD v5/v6 and auth implementation

[pourdaavar]

Summary

• Sync @rineex/ddd README with v5/v6 API (Result union, registry-backed DomainError, Result.ok() void overload, layer contract)
• Fix root README anchors, project tree, VO list, prerequisites, and add documentation map
• Rewrite auth-core design docs to match implemented model; preserve aspirational spec in FUTURE.md
• Update domain errors/VOs READMEs for v6 registry pattern (no type field)
• Fix passwordless docs for Result v5 API; add OTP README; cross-link pg-slonik docs

Closes #70

Test plan

• Pre-commit hooks pass (prettier, cspell)
• Manual link-check: root README → ddd README anchors
• Spot-read public exports vs packages/ddd/src/index.ts and packages/authentication/core/src/index.ts
• Grep confirms no stale Result.fail or error.type in user-facing docs

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