docs: add Russian translation README_ru.md

[a-rybnikov]

Summary

Adds a Russian translation of the project README and updates the language switcher across the existing localized README files so the Russian variant is discoverable from any language version.

• New: README_ru.md — full Russian translation of README.md (425 lines)
• Updated: language switcher in README.md, README_zh.md, README_ja.md, README_ko.md, README_fr.md, README_de.md — one line each, adding | [Русский](README_ru.md) at the end

Translation principles applied

To stay maintainable next to the other localized READMEs, the translation preserves the following verbatim (no Russification):

• All code blocks (bash, json, mermaid, python paths)
• Tool / framework / library names: LangGraph, LangChain, Ollama, ChromaDB, LightRAG, FastAPI, Pydantic, SQLModel, Docling, OpenAI, Claude, Qwen, vLLM, OpenClaw, Cursor, Claude Desktop
• Acronyms: SSDLC, RAG, MCP, SAST, DAST, STRIDE, DREAD, SDR, HITL, OWASP, CIS, CVE, ISO 27001, PCI DSS, SOC2, GDPR, AAD, ServiceNow, CI/CD
• Configuration variable names (LLM_PROVIDER, CHROMA_PERSIST_DIR, etc.)
• File paths and URLs
• All Mermaid architecture diagram identifiers (node names kept English so the diagram stays consistent across localizations)

What was translated: explanatory prose, section headings, table cell descriptions, code-block comments where they explain steps to the reader, and table header words.

Structure

README_ru.md follows the exact same structure and section order as README.md, so the localized versions stay parallel and easy to keep in sync going forward.

Verification

• git diff --stat — 7 files changed, 431 insertions, 6 deletions
• Manually verified the language switcher line appears with Русский in all 6 existing READMEs and the new Russian one
• All anchor / file links in the new file point to the same targets as their English counterparts (relative paths preserved)
• Mermaid diagram syntax preserved verbatim — the identifiers (Router, A1..A6, Cloud, Local) stay English; only the surrounding subgraph labels and a few node display strings are localized where they were already free-text in the English version

AI-assisted disclosure

Pair-developed with Claude Code (Anthropic Opus 4.7) per the CONTRIBUTING_WITH_AI.md guidelines. The translation was drafted with the AI, then reviewed line-by-line against the English source to verify:

• Terminology consistency (Russian academic register, not colloquial)
• Code block / tool name preservation
• Anchor link preservation
• Table column alignment

A native Russian speaker (the submitter) reviewed the final text.

If you'd prefer this PR split into two — one for README_ru.md and one for the 6 language-switcher updates — I can rebase that way; happy to do whichever is easier to review.