feature: migrate to npm workspaces

[levivilet]

Summary

• replace Lerna bootstrap and task orchestration with npm workspaces
• consolidate package lockfiles into the root lockfile while preserving all 27 retained direct dependency resolutions
• update CI, cache-key generation, dependency updates, and hoisted dependency paths for the workspace install

Verification

• nice npm ci
• npm run build
• npm run build:static
• npm test (110 suites, 322 tests)
• npm run test-integration
• npm run type-check
• npm run lint
• direct dependency resolution audit: 27 checked, 0 mismatches