feat: Add case review messaging system with feedback and query capabilities

- Introduced CaseReviewMessage model to handle feedback and queries for cases.
- Implemented views for displaying user and CID messages, including outstanding feedback.
- Created templates for collection feedback overview and user messages.
- Added functionality for acknowledging messages and sending feedback or queries.
- Enhanced collection detail view to show outstanding messages and user message statistics.
- Added tests for handling duplicate DICOM uploads without series.

atlas/models.py

@@ -2024,6 +2024,71 @@ class SelfReview(models.Model):
         )
 
 
+class CaseReviewMessage(models.Model):
+    """Conversation message for one learner attempt on one case.
+
+    Supervisors/collection authors use this for per-case feedback and replies.
+    Learners use it to raise questions/queries. Supervisor messages may require
+    acknowledgement so they continue to flag on the learner-facing pages until
+    explicitly acknowledged.
+    """
+
+    class MessageType(models.TextChoices):
+        FEEDBACK = "feedback", _("Feedback")
+        QUERY = "query", _("Query")
+        REPLY = "reply", _("Reply")
+
+    cid_user_exam = models.ForeignKey(
+        CidUserExam,
+        on_delete=models.CASCADE,
+        related_name="case_review_messages",
+    )
+    case = models.ForeignKey(
+        Case,
+        on_delete=models.CASCADE,
+        related_name="case_review_messages",
+    )
+    author = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="case_review_messages_authored",
+        null=True,
+        blank=True,
+    )
+    author_label = models.CharField(max_length=255, blank=True)
+    message_type = models.CharField(
+        max_length=20,
+        choices=MessageType.choices,
+        default=MessageType.QUERY,
+    )
+    message = models.TextField()
+    requires_acknowledgement = models.BooleanField(default=False)
+    acknowledged_at = models.DateTimeField(null=True, blank=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        ordering = ("created_at",)
+
+    def __str__(self) -> str:
+        return f"{self.get_message_type_display()} for {self.case}"
+
+    @property
+    def is_acknowledged(self) -> bool:
+        return self.acknowledged_at is not None
+
+    def get_author_display(self) -> str:
+        if self.author is not None:
+            full_name = self.author.get_full_name().strip()
+            return full_name or self.author.username
+        return self.author_label or "Learner"
+
+    def acknowledge(self):
+        if self.acknowledged_at is None:
+            self.acknowledged_at = timezone.now()
+            self.save(update_fields=["acknowledged_at"])
+
+
 class UncategorisedDicom(models.Model):
     # We use image to maintain consitency across apps
     image = models.FileField(upload_to=uncategorised_dicom_directory_path)