chore(deploy): dockerize the frontend and backend applications

[Zafar7645]

Summary

Dockerizes both the frontend and backend so the full stack (Postgres, backend, frontend) can be run with a single docker compose up, and updates project documentation to reflect the new workflow.

Type of Change

• Bug fix
• New feature
• Refactor (no behaviour change)
• Documentation
• Chore (deps, tooling, CI)

Related Issue

Closes #11

Changes

• Add apps/backend/Dockerfile: multi-stage build using nest build (webpack) to bundle all dependencies into a single dist/main.js, so the runtime image ships no node_modules and runs as the unprivileged node user
• Add apps/frontend/Dockerfile: builds the Angular app and serves the static browser/ output via nginx
• Add apps/frontend/nginx.conf.template, rendered from BACKEND_HOST/BACKEND_PORT at container start, proxying /api/* to the backend container
• Add docker-compose.yml wiring db (Postgres 16, bound to 127.0.0.1 only), backend, and frontend services with healthchecks and startup ordering (depends_on: condition: service_healthy)
• Add root .env.example for Docker Compose config (DB_USERNAME, DB_PASSWORD, DB_DATABASE, JWT_SECRET, BCRYPT_SALT_ROUNDS, ALLOWED_ORIGIN, and host port overrides DB_PORT/BACKEND_PORT/FRONTEND_PORT) — separate from apps/backend/.env used by the native workflow
• Add .dockerignore
• Bump apps/frontend/package.json and apps/frontend/src/environments/environment.production.ts for the containerized build
• Update CLAUDE.md, README.md, docs/architecture/high-level-design.md, and docs/srs.md to document the Docker workflow alongside the existing native workflow
• Update CHANGELOG.md under [Unreleased] with the new infrastructure additions

Testing

• npm run lint passes with no errors
• Backend unit tests pass (cd apps/backend && npm test)
• Manually tested the affected flow end-to-end
• Added or updated tests for new logic

Manual verification: docker compose up -d --build brings up db, backend, frontend in order (backend waits on Postgres healthcheck, frontend waits on backend healthcheck); registered/logged in through http://localhost:4200 and confirmed the Kanban board loads with /api/* correctly proxied to the backend container.

Screenshots

N/A — no UI change.

Notes for Reviewer

• DB_USERNAME/DB_PASSWORD in .env only take effect the first time the pgdata volume is created; changing them later requires docker compose down -v, which drops the volume — called out in both .env.example and docker-compose.yml.
• Postgres is bound to 127.0.0.1 only and is not reachable from outside the host.
• This is additive: the existing native workflow (npm run start:backend / start:frontend against apps/backend/.env) is untouched.