Align repository with technical guide and fix CI workflow

[IndexGrid]

This PR comprehensively aligns the repository with the 'AI-Driven-Implementation-technical-guide.md' and resolves critical CI/CD issues.

Key Improvements:

1. Documentation & Transparency:
   • Replaced boilerplate READMEs with project-specific documentation.
   • Created docs/ADR/ (Architecture Decision Records) to document key technical choices (Monorepo, Zod).
   • Added a structured CHANGELOG.md following 'Keep a Changelog' standards.
2. Runtime Contract Hardening:
   • Implemented ZodValidationPipe in NestJS to enforce the shared Zod schema at the transport boundary.
   • Ensured 100% type-safety and runtime validation between Client and Server.
3. Database Discipline:
   • Replaced manual init.sql with versioned Prisma migrations.
   • Automated migration deployment in Docker and CI environments.
4. Test Matrix Expansion:
   • Switched frontend tests to Vitest for consistency.
   • Achieved 100% test coverage for the backend synchronization module.
   • Added integration tests for the frontend sync runner, covering stale item recovery and partial failures.
5. CI/CD Hardening:
   • Fixed native binding issues for lightningcss and @tailwindcss/oxide in Linux CI.
   • Implemented strict quality gates: Typecheck, Lint, Test Coverage, and Migration checks.
   • Added automated release draft generation.

Verified locally: All tests passing, builds successful, and documentation is up to date.