feat(api): add stream CRUD REST endpoints (#5)

[nanaf6203-bit]

Closes #5

Implements full CRUD REST endpoints for streams at api/src/streams/:

• POST /streams — Create a new stream (auth required)
• GET /streams — List streams with pagination and optional status filter (auth required)
• GET /streams/:id — Get a single stream (ownership required)
• PATCH /streams/:id — Partial update with status transition validation (ownership required)
• DELETE /streams/:id — Delete a stream (ownership required)

What was done

• Created StreamsModule with entity, DTOs, repository, service, and controller following existing TagsModule patterns
• Added AuthGuard in common/guards/ for user extraction from X-User-Id header (placeholder until JWT auth pipeline lands)
• Endpoints protected with AuthGuard (create/list) and StreamOwnershipGuard (read/update/delete)
• Status transition validation: inactive<->active, *->error, error->inactive
• Full Swagger/OpenAPI documentation with all response decorators
• TypeScript typecheck passes cleanly

[Xhristin3]

LGTM