perf(json-document): harden adapter-scale validation

[developer-1px]

Summary

• add checked structural-schema local validation for supported single and independent replacements
• preserve full-candidate isolation for custom/refined schemas and clone local object inputs before Zod validation
• retain overlapping-batch final-state semantics and aggregate independent validation issues
• add Canvas/Editable-shaped CPU p95 readiness gates with wall-time diagnostics

Verification

• npm run verify
• npm run docs:evaluate
• npm run standard:check
• npm run perf:adapters
• npm run perf:core
• npm run perf:causal
• packed Canvas: 48 DesignDocument tests + official 1k/5k/10k benchmark
• packed Editable: 132 package tests + 90 Chromium/Firefox/WebKit tests
• public contract and package exports unchanged