Complete zh-CN translations - add missing keys across 6 files

[1y4w1s]

This PR completes the Simplified Chinese (zh-CN) translations by adding ~86 missing keys across 6 files, making it 100% coverage.

Changes

File	Keys Added	Notes
chat.json	6	clearLastUsedModel, speculativeDecoding stats, plugin auth
config.json	31 + 12 renamed	numParallelSessions, useUnifiedKvCache, contextCheckpoints, autoFit, budgetTokens; commitChanges→saveChanges
developer.json	17	allowMcp section (title/hint/modes), lmStudioRestV1 endpoints, Anthropic-compatible
models.json	15	loader.guardrails memory warnings section, virtual.altsSelect
settings.json	16	appNavigationBarPosition (top/left), defaultContextLength, jitTTL, autoFitMinContextLength, modelDefaultsLabel
shared.json	1	beta
sidebar.json	fix	运行时间 → 运行环境 (consistency with developer.json)
discover.json	fix	Updated search placeholder from Hugging Face to local models

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