docs: adjustment to API docs and alternative patterns added

[ihorman]

Restructure API documentation and add alternative patterns

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Description

Restructured documentation to separate REST from alternative API patterns and enhanced existing sections with comprehensive details:

Restructuring:

• Moved GraphQL, gRPC, and AsyncAPI out of REST/API.md into separate directories
• Created GraphQL/, gRPC/, and AsyncAPI/ directories with dedicated API.md files
• Updated README.md with clear navigation structure

REST Enhancements (additive only, no deletions):

• Authentication & Authorization: Added OAuth2 flows, API key rotation, JWT claims, mTLS details, RBAC/ABAC patterns
• Retry Strategies: Added exponential backoff, jitter, circuit breaker, timeout handling
• Webhooks: Added replay protection, signature verification, delivery guarantees, management endpoints
• OpenAPI: Added documentation requirements, schema design patterns, SDK generation guidelines
• Versioning: Added link to VERSIONING.md for complete details

Alternative API Patterns (new):

• GraphQL: Schema design, N+1 prevention, directives, persisted queries, federation, error handling
• gRPC: Protocol Buffers, streaming patterns, backward compatibility, service mesh, error handling
• AsyncAPI: Event-driven architecture, CQRS, saga patterns, DLQ, event monitoring

Bug Fixes:

• Fixed STATUS_CODES.md header format (### → #)
• Fixed PAGINATION.md to preserve original format with alternative envelope note

Type of Change

• Documentation update
• New section/guide
• Bug fix (typo, broken link)
• Code example improvement
• Other:

Checklist

• Commits are signed off (git commit -s)
• Changes follow DNA principles (additive changes, preserved existing content)
• Code examples tested (all examples are syntactically correct)
• Links are valid (verified cross-references)
• Self-review completed
• No Russian text (verified with grep)

Related Issues

Comprehensive API documentation coverage:

• ✅ REST (resources, pagination, filtering)
• ✅ Errors (Problem+JSON, trace IDs)
• ✅ Versioning & deprecations
• ✅ Idempotency & retries
• ✅ AuthN/AuthZ (API keys, OAuth2/OIDC, JWT, mTLS, scopes)
• ✅ GraphQL (schema design, N+1, directives, persisted queries)
• ✅ gRPC & Async APIs (contracts, streaming, compatibility)
• ✅ Webhooks (signatures, replay protection, dead-letter)
• ✅ Documentation (OpenAPI/AsyncAPI, SDKs, examples)

Files Changed

• README.md - Updated structure with REST/GraphQL/gRPC/AsyncAPI sections
• REST/API.md - Enhanced with retry strategies, auth details, webhooks, removed non-REST sections
• REST/PAGINATION.md - Added alternative envelope format note
• REST/STATUS_CODES.md - Fixed header format
• GraphQL/API.md - New file with GraphQL guidelines
• gRPC/API.md - New file with gRPC guidelines
• AsyncAPI/API.md - New file with AsyncAPI guidelines