# CRM Step 02 — Backend: Customers CRUD

## Context
Read `.claude/crm-build-plan.md` first for full data models, conventions, and IMPORTANT NOTES.
Step 01 must be complete (`backend/crm/` module exists).

## Task
Add Customers models, service, and router to `backend/crm/`.

## What to build

### 1. Add to `backend/crm/models.py`

**Contact entry:**
- `ContactType` enum — email, phone, whatsapp, other
- `CustomerContact` — type (ContactType), label (str, e.g. "personal"/"church"), value (str), primary (bool default False)

**Note entry:**
- `CustomerNote` — text (str), by (str), at (str ISO datetime)

**Owned items (3 tiers):**
- `OwnedItemType` enum — console_device, product, freetext
- `OwnedItem`:
  - type: OwnedItemType
  - For console_device: device_id (Optional[str]), label (Optional[str])
  - For product: product_id (Optional[str]), product_name (Optional[str]), quantity (Optional[int]), serial_numbers (Optional[List[str]])
  - For freetext: description (Optional[str]), serial_number (Optional[str]), notes (Optional[str])

**Location:**
- `CustomerLocation` — city (Optional[str]), country (Optional[str]), region (Optional[str])

**Customer models:**
- `CustomerCreate` — name (str), organization (Optional[str]), contacts (List[CustomerContact] default []), notes (List[CustomerNote] default []), location (Optional[CustomerLocation]), language (str default "el"), tags (List[str] default []), owned_items (List[OwnedItem] default []), linked_user_ids (List[str] default []), nextcloud_folder (Optional[str])
- `CustomerUpdate` — all fields Optional
- `CustomerInDB` — extends CustomerCreate + id, created_at, updated_at
- `CustomerListResponse` — customers: List[CustomerInDB], total: int

### 2. Add to `backend/crm/service.py`
Firestore collection: `crm_customers`
Functions:
- `list_customers(search=None, tag=None) -> List[CustomerInDB]`
  - search matches against name, organization, and any contact value
- `get_customer(customer_id) -> CustomerInDB` — 404 if not found
- `create_customer(data: CustomerCreate) -> CustomerInDB`
- `update_customer(customer_id, data: CustomerUpdate) -> CustomerInDB`
- `delete_customer(customer_id) -> None`

### 3. Add to `backend/crm/router.py`
Add a second router or extend existing file with prefix `/api/crm/customers`:
- `GET /` — list_customers (query: search, tag)
- `GET /{customer_id}` — get_customer
- `POST /` — create_customer
- `PUT /{customer_id}` — update_customer
- `DELETE /{customer_id}` — delete_customer

Register this router in `backend/main.py` alongside the products router.

## Notes
- OwnedItem is a flexible struct — store all fields, service doesn't validate which fields are relevant per type (frontend handles that)
- linked_user_ids are Firebase Auth UIDs (strings) — no validation needed here, just store them
- Search in list_customers: do client-side filter after fetching all (small dataset)