test: add parser-safe validation for mock API modules

[Divine-mercyx]

Summary

• Register mock API domains as independently parseable modules with a stable export contract.
• Add focused node:test checks that parse each domain in isolation, so a syntax error in one domain stays scoped to that file.
• Keep public MockAccessApi methods and aggregator re-exports stable for existing consumers (lib/api/index.ts, components/nav.tsx).

Type of Change

• Bug fix
• New feature
• Tech-debt / structure
• CI/CD

Changes Made

• Added lib/api/mock/domains.ts as the canonical domain/export registry.
• Added test/mock-api-structure.test.ts using TypeScript syntactic diagnostics with noResolve (parser-safe, no typecheck of imports).
• Included lib/api/mock/**/*.ts in the existing test tsconfig so domain modules participate in the current test pipeline.
• No GitHub Actions or CI workflow changes.

Acceptance Criteria

• Mock API domains have clearly defined module boundaries.
• A syntax error in one domain is reported against that file only and does not require editing a 2,000+ line monolith.
• Public mock API exports remain stable for existing consumers.
• Focused automated verification uses the repository's existing node:test + test/tsconfig.json conventions.
• No GitHub Actions or CI/CD changes.

Test Coverage

• npx tsc -p test/tsconfig.json --skipLibCheck
• node --test test-dist/test/mock-api-structure.test.js

Closes #386

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