docs: add Chinese (zh) translations for key documentation

[maojianian25-png]

Summary

Add Chinese translations for three core documentation files to lower the barrier for Chinese-speaking developers and node operators to participate in the Gonka network.

Changes

New files in docs/zh/:

File	Source	Description
docs/zh/consumer_setup.md	docs/consumer_setup.md	Consumer setup guide — account creation, funding, public key publishing, and sending inference requests
docs/zh/join_chain.md	docs/join_chain.md	Chain node setup guide — prerequisites, config.env, NODE_CONFIG, launching and customizing deployment
docs/zh/gonka_poc.md	docs/gonka_poc.md	Proof of Compute design — system architecture, 5-stage PoC workflow, dual power systems, Cosmos SDK integration

Translation approach

• All technical terms (PoC, epoch, MLNode, Cosmos SDK, CometBFT, etc.) are preserved in their original English form for clarity
• Code blocks, commands, and file paths are kept identical to the originals
• Table formatting and document structure mirror the English versions
• Links to external resources are preserved

Motivation

Chinese is one of the largest developer communities globally. Providing documentation in Chinese aligns with the Gonka bounty program goal of expanding network accessibility through translations.

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Bounty reference: Documentation/Translation (20–200 GNK) — https://joingonka.ai/en/knowledge/bounty/