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/serializers.py

@@ -2,11 +2,14 @@ from rest_framework import serializers
 import re
 from pathlib import Path
 from decimal import Decimal, InvalidOperation
+from django.contrib.auth import get_user_model
 from django.urls import reverse
 from django.utils import timezone
+from modules.task_management.models import Task
 from .models import (
     Crane,
     Vehicle,
+    ServiceContextNote,
     VehicleNotification,
     WorkOrder,
     WorkOrderAdditionalCostsTable,
@@ -18,6 +21,8 @@ from .models import (
 )
 from . import services
 
+User = get_user_model()
+
 
 class VehicleSerializer(serializers.ModelSerializer):
     # Čitljivo ime klijenta — read-only, za prikaz u frontendu i adminu
@@ -95,6 +100,134 @@ class VehicleNotificationSerializer(serializers.ModelSerializer):
         read_only_fields = ['id', 'title', 'message', 'metadata', 'level', 'is_sent', 'created_at']
         # is_read is writable via the "mark_read" action, but normally read-only in list
 
+
+class ServiceContextNoteSerializer(serializers.ModelSerializer):
+    created_by_name = serializers.SerializerMethodField()
+    recipient_name = serializers.SerializerMethodField()
+    work_order_label = serializers.SerializerMethodField()
+    task_title = serializers.SerializerMethodField()
+
+    class Meta:
+        model = ServiceContextNote
+        fields = [
+            'id',
+            'created_by',
+            'created_by_name',
+            'recipient',
+            'recipient_name',
+            'audience_source',
+            'work_order',
+            'work_order_label',
+            'task',
+            'task_title',
+            'note',
+            'note_date',
+            'is_closed',
+            'closed_at',
+            'created_at',
+            'updated_at',
+        ]
+        read_only_fields = fields
+
+    def get_created_by_name(self, obj):
+        return obj.created_by.get_full_name() or obj.created_by.email
+
+    def get_recipient_name(self, obj):
+        return obj.recipient.get_full_name() or obj.recipient.email
+
+    def get_work_order_label(self, obj):
+        if not obj.work_order_id:
+            return None
+        display_code = str(getattr(obj.work_order, 'display_code', '') or '').strip().upper()
+        return display_code or f"WO-{obj.work_order_id}"
+
+    def get_task_title(self, obj):
+        if not obj.task_id:
+            return None
+        return obj.task.title
+
+
+class ServiceContextNoteCreateSerializer(serializers.Serializer):
+    AUDIENCE_CHOICES = ['self', 'member', 'team']
+
+    note = serializers.CharField(required=True, allow_blank=False, trim_whitespace=True)
+    note_date = serializers.DateField(required=False, allow_null=True)
+    audience = serializers.ChoiceField(choices=AUDIENCE_CHOICES, default='self')
+    target_user = serializers.PrimaryKeyRelatedField(
+        queryset=User.objects.filter(is_active=True),
+        required=False,
+        allow_null=True,
+    )
+    target_users = serializers.ListField(
+        child=serializers.PrimaryKeyRelatedField(queryset=User.objects.filter(is_active=True)),
+        required=False,
+        allow_empty=False,
+    )
+    work_order = serializers.PrimaryKeyRelatedField(
+        queryset=WorkOrder.objects.filter(is_active=True),
+        required=False,
+        allow_null=True,
+    )
+    task = serializers.PrimaryKeyRelatedField(
+        queryset=Task.objects.filter(is_active=True),
+        required=False,
+        allow_null=True,
+    )
+
+    def validate(self, attrs):
+        request = self.context.get('request')
+        user = getattr(request, 'user', None)
+        if user is None:
+            raise serializers.ValidationError('Autentikacija je obavezna.')
+
+        audience = attrs.get('audience', 'self')
+        target_user = attrs.get('target_user')
+        target_users = attrs.get('target_users') or []
+        work_order = attrs.get('work_order')
+        task = attrs.get('task')
+        note = str(attrs.get('note', '') or '').strip()
+        can_manage_recipients = bool(
+            getattr(user, 'is_serviser', False)
+            or getattr(user, 'is_staff', False)
+            or (getattr(user, 'is_team_member', False) and not getattr(user, 'is_serviser', False))
+        )
+
+        if not note:
+            raise serializers.ValidationError({'note': 'Bilješka ne može biti prazna.'})
+
+        if not can_manage_recipients and audience != 'self':
+            raise serializers.ValidationError({'audience': 'Samo supervisor ili serviser može slati bilješke drugim članovima tima.'})
+        if audience == 'member' and not target_user and len(target_users) == 0:
+            raise serializers.ValidationError({'target_users': 'Odaberite barem jednog servisera.'})
+        if audience in {'self', 'team'} and target_user:
+            raise serializers.ValidationError({'target_user': 'Odabrani tip publike ne koristi ciljano polje člana tima.'})
+        if audience in {'self', 'team'} and len(target_users) > 0:
+            raise serializers.ValidationError({'target_users': 'Odabrani tip publike ne koristi listu servisera.'})
+        if target_user and not getattr(target_user, 'is_serviser', False):
+            raise serializers.ValidationError({'target_user': 'Bilješku je moguće poslati samo serviseru.'})
+        for selected_user in target_users:
+            if not getattr(selected_user, 'is_serviser', False):
+                raise serializers.ValidationError({'target_users': 'Bilješku je moguće poslati samo serviserima.'})
+
+        if work_order:
+            if not work_order.is_active or str(work_order.status or '').lower() != 'open':
+                raise serializers.ValidationError({'work_order': 'Moguće je povezati samo aktivni otvoreni putni nalog.'})
+
+        if task:
+            status = str(task.status or '').lower()
+            if status in {'zavrsen', 'neaktivan'}:
+                raise serializers.ValidationError({'task': 'Moguće je povezati samo aktivni radni zadatak.'})
+
+        if task and work_order and task.work_order_id and str(task.work_order_id) != str(work_order.id):
+            raise serializers.ValidationError({'task': 'Radni zadatak ne pripada odabranom putnom nalogu.'})
+
+        attrs['note'] = note
+        if task and not work_order and task.work_order_id:
+            attrs['work_order'] = task.work_order
+        if audience == 'member' and len(target_users) == 0 and target_user:
+            attrs['target_users'] = [target_user]
+        return attrs
+
 class WorkOrderSerializer(serializers.ModelSerializer):
     crane = serializers.SerializerMethodField()
     crane_label = serializers.SerializerMethodField()