feat: dodaj bilješke widget i admin kalendar/notifikacije

Uveden je novi Notes drawer s kalendar integracijom, zajednički DRY
left-slide mehanizam te međusobno isključivo prikazivanje s Kalendar
widgetom.

Backend i frontend su prošireni za servisne bilješke (uključujući slanje
na više servisera), dodan je users/servicers endpoint, te su uvedene
warning notifikacije kada serviser ima više od 2 zadatka isti dan.

U admin su dodane stavke za Bilješke i zaseban Kalendar zadataka (proxy
TaskCalendar) radi lakšeg operativnog pregleda.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/modules/fleet/views.py

@@ -2,9 +2,11 @@
 
 from io import BytesIO
 import base64
+from collections import OrderedDict
 from datetime import timedelta
 from pathlib import Path
 from decimal import Decimal, InvalidOperation
+from django.contrib.auth import get_user_model
 
 from PIL import Image, UnidentifiedImageError
 from django.conf import settings
@@ -14,6 +16,7 @@ from django.urls import reverse
 from django.utils import timezone
 from django.utils.html import escape
 from django.db.models import Q
+from django.db import transaction
 from reportlab.lib.pagesizes import A4
 from reportlab.lib import colors
 from reportlab.lib.utils import ImageReader
@@ -21,7 +24,7 @@ from reportlab.lib.styles import getSampleStyleSheet
 from reportlab.pdfgen import canvas
 from reportlab.platypus import Table, TableStyle, Paragraph
 from .pdf_layout import register_unicode_fonts, draw_standard_header_footer
-from rest_framework import viewsets, permissions, status
+from rest_framework import viewsets, permissions, status, mixins
 from rest_framework.decorators import action, api_view, permission_classes
 from rest_framework.response import Response
 from rest_framework.exceptions import PermissionDenied, ValidationError as DRFValidationError
@@ -32,6 +35,7 @@ from .models import (
     Crane,
     Vehicle,
     VehicleNotification,
+    ServiceContextNote,
     WorkOrder,
     WorkOrderPhoto,
     GeneratedWorkOrderPdf,
@@ -50,6 +54,8 @@ from .serializers import (
     WorkOrderPhotoSerializer,
     VehicleServiceRecordSerializer,
     VehicleNotificationSerializer,
+    ServiceContextNoteSerializer,
+    ServiceContextNoteCreateSerializer,
     VehicleServicePhotoSerializer,
     VehicleServiceAttachmentSerializer,
 )
@@ -67,6 +73,7 @@ from .tasks import (
 )
 
 register_unicode_fonts()
+User = get_user_model()
 
 def _fleet_assets_queryset_for_user(user, model, *, asset_type=None):
     queryset = model.objects.select_related('client', 'assigned_servicer').filter(is_active=True)
@@ -99,6 +106,23 @@ def _work_orders_queryset_for_user(user):
     return queryset.filter(creator=user)
 
 
+def _is_supervisor_user(user):
+    return bool(getattr(user, 'is_staff', False) or (getattr(user, 'is_team_member', False) and not getattr(user, 'is_serviser', False)))
+
+
+def _active_team_members_queryset():
+    return User.objects.filter(is_active=True, is_team_member=True).order_by('first_name', 'last_name', 'email')
+
+
+def _service_context_notes_queryset_for_user(user):
+    return (
+        ServiceContextNote.objects
+        .select_related('created_by', 'recipient', 'work_order', 'task')
+        .filter(is_active=True, recipient=user, is_closed=False)
+        .order_by('note_date', '-created_at')
+    )
+
+
 def _work_order_related_tasks_queryset(work_order):
     from modules.task_management.models import Task
 
@@ -1994,6 +2018,110 @@ class WorkOrderInvoiceViewSet(viewsets.ModelViewSet):
         instance.is_active = False
         instance.save(update_fields=['is_active'])
 
+
+class ServiceContextNoteViewSet(
+    mixins.ListModelMixin,
+    mixins.CreateModelMixin,
+    viewsets.GenericViewSet,
+):
+    permission_classes = [permissions.IsAuthenticated]
+
+    def get_queryset(self):
+        return _service_context_notes_queryset_for_user(self.request.user)
+
+    def get_serializer_class(self):
+        if self.action == 'create':
+            return ServiceContextNoteCreateSerializer
+        return ServiceContextNoteSerializer
+
+    def create(self, request, *args, **kwargs):
+        serializer = self.get_serializer(data=request.data, context={'request': request})
+        serializer.is_valid(raise_exception=True)
+        payload = serializer.validated_data
+        user = request.user
+        audience = payload.get('audience', 'self')
+        target_users = payload.get('target_users') or []
+        note_text = payload.get('note')
+        note_date = payload.get('note_date')
+        work_order = payload.get('work_order')
+        task = payload.get('task')
+        is_supervisor = _is_supervisor_user(user)
+        can_manage_recipients = bool(is_supervisor or getattr(user, 'is_serviser', False))
+
+        if work_order and not _work_orders_queryset_for_user(user).filter(pk=work_order.pk).exists():
+            raise DRFValidationError({'work_order': 'Nemate dozvolu za odabrani putni nalog.'})
+        if task and not is_supervisor and str(getattr(task, 'assigned_to_id', '') or '') != str(user.id):
+            raise DRFValidationError({'task': 'Možete povezati samo svoj aktivni radni zadatak.'})
+
+        recipients = []
+        if audience == 'self':
+            recipients = [user]
+        elif audience == 'member':
+            recipients = list(target_users)
+        else:
+            if not can_manage_recipients:
+                raise DRFValidationError({'audience': 'Nemate dozvolu za slanje bilješke cijelom timu.'})
+            recipients = list(_active_team_members_queryset())
+            if not recipients:
+                raise DRFValidationError({'audience': 'Nema aktivnih članova tima za slanje bilješke.'})
+
+        created_notes = []
+        seen = OrderedDict()
+        for recipient in recipients:
+            seen[str(recipient.id)] = recipient
+        with transaction.atomic():
+            for recipient in seen.values():
+                note = ServiceContextNote.objects.create(
+                    created_by=user,
+                    recipient=recipient,
+                    audience_source=audience,
+                    work_order=work_order,
+                    task=task,
+                    note=note_text,
+                    note_date=note_date,
+                )
+                created_notes.append(note)
+                NotificationService.create_notification(
+                    recipient=recipient,
+                    title='Nova bilješka servisnog konteksta',
+                    message=note_text[:255],
+                    level='info',
+                    metadata={
+                        'entity_type': 'service_note',
+                        'service_note_id': str(note.id),
+                        'work_order_id': str(work_order.id) if work_order else None,
+                        'task_id': str(task.id) if task else None,
+                        'section': 'dashboard',
+                        'note_date': note_date.isoformat() if note_date else None,
+                    },
+                    send_email=False,
+                )
+
+        response_serializer = ServiceContextNoteSerializer(
+            _service_context_notes_queryset_for_user(user)[:20],
+            many=True,
+        )
+        return Response(
+            {
+                'created_count': len(created_notes),
+                'notes': response_serializer.data,
+            },
+            status=status.HTTP_201_CREATED,
+        )
+
+    @action(detail=True, methods=['post'], url_path='close')
+    def close(self, request, pk=None):
+        note = self.get_object()
+        if note.is_closed:
+            serializer = ServiceContextNoteSerializer(note)
+            return Response(serializer.data, status=status.HTTP_200_OK)
+        note.is_closed = True
+        note.closed_at = timezone.now()
+        note.save(update_fields=['is_closed', 'closed_at', 'updated_at'])
+        serializer = ServiceContextNoteSerializer(note)
+        return Response(serializer.data, status=status.HTTP_200_OK)
+
+
 class VehicleNotificationViewSet(viewsets.ReadOnlyModelViewSet):
     """
     List all notifications for the authenticated user and provide an action