feat(events): add Event + User entities, REST API, and MergeAll

[mmm-byte]

Adds a full Events feature on top of the nestjs/typescript-starter boilerplate:

Domain

• Event entity (id, title, description?, status, startTime, endTime, timestamps, ManyToMany invitees)
• User entity (id, name, events: string[], ManyToMany invitedEvents)
• EventStatus enum: TODO | IN_PROGRESS | COMPLETED

API

• POST /events create an event
• GET /events/:id retrieve an event
• DELETE /events/:id delete an event
• POST /users/:id/merge-events MergeAll for a user
  • sweeps the user's events, clusters overlaps
  • creates a single merged event spanning min(start)..max(end)
  • appends titles/descriptions with ' | '
  • picks a 'reasonable' status (IN_PROGRESS > COMPLETED > TODO)
  • union of invitees is preserved
  • deletes the originals and rewrites every invitee's events[] list
• Global ValidationPipe enforces DTO rules

Stack

• @nestjs/typeorm + better-sqlite3 (zero-setup local DB)
• class-validator / class-transformer
• DTO: CreateEventDto, CreateUserDto

Tests (per FAQ #1: both)

• 13 unit tests (mocked TypeORM repositories) across 3 suites
  • events.service.spec.ts
  • events.controller.spec.ts
  • users.controller.spec.ts
• 3 e2e tests against a real SQLite file
  • events.e2e-spec.ts boots the full Nest app + supertest
  • exercises create user, create event, get, merge, delete

Docs

• README.md rewritten with API table, run instructions, curl recipe, and demo-video script

Removes

• src/app.controller.ts, src/app.service.ts, src/app.controller.spec.ts (Hello World boilerplate replaced by the events feature)
• test/app.e2e-spec.ts (replaced by test/events.e2e-spec.ts)