Document the local development bootstrap flow for the backend

[Jumongweb]

Summary

Document the local development bootstrap flow for the backend, smart contracts, and frontend so contributors can start the full stack with repo-accurate steps and environment expectations.

Closes #1057

What Changed

• rewrote docs/LOCAL_DEVELOPMENT_QUICKSTART.md to reflect the actual local bootstrap path
• updated the root README.md quick start to point to the supported backend/frontend/contracts flow
• updated backend/README.md with Prisma migration setup and default SQLite/in-memory local behavior
• replaced the stock Vite template content in frontend/README.md with project-specific setup instructions

Notes

• documented that the default backend local path uses Prisma with SQLite when DATABASE_URL is unset
• documented that Redis-backed features fall back to in-memory behavior when REDIS_URL is unset
• clarified that real contract-backed flows require matching VAULT_CONTRACT_ID values in backend and frontend env files
• made contract setup explicit but optional for contributors who are not changing on-chain code

Validation

• cd backend && npm test -- --runInBand
  • fails on existing backend test issues in src/__tests__/pagination.test.ts and src/__tests__/issues481-484.test.ts
• cd frontend && npm run test:run
  • fails in the current environment because vitest is not installed
• cargo test
  • started successfully and entered compilation, but did not complete before wrap-up

Documentation Updated

• docs/LOCAL_DEVELOPMENT_QUICKSTART.md
• README.md
• backend/README.md
• frontend/README.md

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