build(assets): copy contractErrors and schemas into dist on build (closes #932)

[mopxam-art]

Why

TypeScript (tsc) compiles .ts files to .js in dist but does not copy static JSON assets (src/data/contractErrors.json, src/schemas/creator-application.schema.json). In Docker production builds where only dist/ is copied into the runtime stage, importing src/lib/contractErrors throws MODULE_NOT_FOUND at boot time.

What

• Created asset copy helper scripts/copy-assets.cjs that copies src/data/, src/schemas/, and src/config/ JSON files into dist/.
• Updated package.json build script to chain asset copying: "build": "tsc && node scripts/copy-assets.cjs".
• Added COPY scripts ./scripts in Dockerfile builder stage so assets are populated during container image builds.
• Added comprehensive unit test suite in src/__tests__/buildAssets.test.ts verifying asset presence, schema validation, and error decoding against compiled dist output.

Verified

• All unit tests pass (npx jest src/__tests__/buildAssets.test.ts --forceExit, 102 tests pass).
• Clean TypeScript typecheck (npm run typecheck) and linter (npm run lint).
• Runtime verification: node -e "require('./dist/lib/contractErrors')" succeeds cleanly.

Closes #932