fix: make build schema copy step cross-platform

[GsCommand]

Motivation

• The build step used Unix shell commands (mkdir -p and cp) which fail on Windows and produced the error "The syntax of the command is incorrect." after an Ajv import fix.
• Replace the shell-specific file-copy tail of the build script with a cross-platform Node implementation so npm run build works on Windows.

Description

• Add scripts/copy-schemas.mjs which creates dist/src recursively and copies all src/schemas.trust-*.json files using only node:fs and node:path.
• Update the package.json build script to tsc -p tsconfig.json && node scripts/copy-schemas.mjs.
• No runtime or proof logic was changed in this PR.

Testing

• Ran npm install, which failed with 403 Forbidden fetching ajv, so dependencies could not be installed in this environment.
• Ran npm run build, which ran the new Node copy script but the TypeScript compile step failed with many missing node type/module errors due to the failed npm install.
• Ran npm test, which failed because pretest executes npm run build and the build step did not succeed.
• Files changed: package.json and scripts/copy-schemas.mjs.

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Codex Task