v0.1.20 — README refresh + Russian and Ukrainian translations

Added

• Russian and Ukrainian READMEs. Full translations (README.ru.md, README.ua.md) pinned to v0.1.19, with a language switcher in all three files.

Changed

• README refreshed for v0.1.16–19. Fixed the stale model lineup (gemini-3-flash-preview → gpt-oss:120b in the fusion-coder panel; glm-5.2 on the fusion-agents simple route), documented the agent-loop reliability features (synth completeness guard with judge fallback + SSE keepalive, honest max_tokens stop_reason, per-model concurrency budgets, separated background-traffic class), updated concurrency/timeout numbers to the shipped presets, added FUSION_SYNTH_RECOVERY_PING_MS to the environment table, removed a dangling Docker cross-reference.