docs: add bilingual DLC packaging guidance

[nowaytofindavailableone]

Summary

• Add a Russian DLC overview and a Russian DLC/mod packaging guide.
• Add English counterparts with reviewed RU↔EN terminology and explicit notes for intentional canonical-Russian links.
• Add the permanent AGENTS.md bilingual-cycle/review/parallel-work pipeline.
• Preserve REDkit identifiers, paths, extensions, warnings, limitations, and source traceability.

Sources

• Official CD PROJEKT RED documentation: https://cdprojektred.atlassian.net/wiki/spaces/W3REDkit/pages/6328346
• Official CD PROJEKT RED documentation: https://cdprojektred.atlassian.net/wiki/spaces/W3REDkit/pages/6327243
• Canonical REDkit Open Documentation references and DLC steps under https://github.com/redkit-resources/docs/tree/main/docs/unofficial_docs/.

Review and validation

• Pass A successful retry A5: independent fact/safety PASS and translation PASS.
• Initial Pass B B1 was blocked by translation clarity findings; coordinator fixed them and created immutable retry bundle pass-B2.
• Pass B2: independent fact/safety PASS (B-fact-20260914-02) and English translation/parity PASS (B-translation-20260914-02).
• Reviewed immutable B2 bundle SHA-256: 0FCE4EE1C54A3720D86C722E3A0167735E12BB51A15BF9868939CE5B0E5FA005.
• git diff --check: PASS; staged allowlist/blob checks: PASS.
• Static changed-page Markdown link check: PASS (46 link tokens, 5 local targets checked); RU/EN navigation target check: PASS (77 targets).
• Isolated Python 3.11.9 / MkDocs 1.6.1 non-strict RU and EN builds: PASS, outputs outside the repository.
• Strict builds were attempted but are not green because the repository's existing nav mappings are rejected as configuration warnings by MkDocs 1.6.1 strict mode; this cycle does not broaden scope to rewrite the baseline navigation schema. Non-strict builds completed successfully with the baseline warnings recorded.
• REDkit and the test game were not run; this PR claims documentation/static validation only.

Scope

Base: redkit-resources/docs:main
Head: nowaytofindavailableone:$branch

No merge or auto-merge is requested.