feat: EventRegistration entity + public signup endpoint + coordinator view + CSV export

[nadavosa]

Context

Linked to need4deed-org/fe#647 — in-house event registration replacing Google Forms.

New entity: EventRegistration

Field	Type	Notes
id	number	PK
opportunityId	number	FK → opportunity (must be dated + non-accompanying)
fullName	string
email	string
phone	string | null
numberOfPeople	number	default 1
languagePreference	string | null
message	string | null	max 500 chars
createdAt	timestamp

Endpoints

POST /event-registration (public, no auth)

Anyone can submit. Validate that the opportunity exists, has an appointmentDate, and is not past.

Body:
```json
{
"opportunityId": 5,
"fullName": "Ali K.",
"email": "ali@example.com",
"phone": "+49123456",
"numberOfPeople": 2,
"languagePreference": "Arabic",
"message": "Looking forward to it"
}
```

Response: `201 { message: "Registration submitted." }`

Errors:

• `404` — opportunity not found
• `400` — opportunity is not an event (no date, or accompanying type)
• `400` — event date is in the past

GET /opportunity/:id/registrations (COORDINATOR, NGO, ADMIN only)

Returns all registrations for a given event opportunity, ordered by `createdAt DESC`.

Response:
```json
{
"data": [
{
"id": 1,
"fullName": "Ali K.",
"email": "ali@example.com",
"phone": "+49123456",
"numberOfPeople": 2,
"languagePreference": "Arabic",
"message": "...",
"createdAt": "2026-06-13T10:00:00Z"
}
],
"count": 1,
"totalPeople": 2
}
```

Include `totalPeople` (sum of numberOfPeople across all registrations).

GET /opportunity/:id/registrations/export (COORDINATOR, NGO, ADMIN only)

Returns a CSV file download.

Headers: `Content-Type: text/csv`, `Content-Disposition: attachment; filename="registrations-{id}.csv"`

Columns: Name, Email, Phone, People, Language, Message, Registered at

SDK types

Add to need4deed-sdk:

• `ApiEventRegistrationPost`
• `ApiEventRegistrationGet`

Tasks

• `EventRegistration` entity (TypeORM)
• Repository
• `POST /event-registration` (public route, no auth hook)
• `GET /opportunity/:id/registrations` (auth: COORDINATOR, NGO, ADMIN)
• `GET /opportunity/:id/registrations/export` — CSV
• Validation: opportunity must be a dated non-accompanying event, not in the past
• SDK types