fix(jira,tests): send real datetime to RT/BT date fields, resolve assignee usernames for operators

- RT/BT Start/End Date are genuine Jira "datetime" custom fields (confirmed
  via issue_editmeta), not plain dates. Pushing a bare "YYYY-MM-DD" string
  made Jira default the time-of-day to midnight, so RT Start Date and RT
  End Date ended up showing the same meaningless midnight timestamp instead
  of the actual execution window. Now sends a full ISO datetime.
- The test detail page showed "RT: Unassigned" for the operator who WAS
  correctly assigned, because GET /users/operators (the only source
  AssigneeControl used to resolve an assignee ID into a username) is
  restricted to leads/managers — a plain operator has no other way to
  resolve their own ID. TestOut now resolves and includes the assignee's
  username directly (red/blue tech + reviewer), so the badge no longer
  depends on a permission-gated list the viewer might not have access to.

backend/app/schemas/test.py

@@ -330,6 +330,12 @@ class TestOut(BaseModel):
     # Assignment fields
     red_tech_assignee: uuid.UUID | None = None
     blue_tech_assignee: uuid.UUID | None = None
+    # Resolved usernames — the operator (or lead) viewing a test they're not
+    # a lead/manager on can't call GET /users/operators (403), so they have
+    # no other way to resolve who an assignee ID actually is. Populated
+    # from the ORM relationship, same pattern as technique_name below.
+    red_tech_assignee_username: str | None = None
+    blue_tech_assignee_username: str | None = None
 
     # Review assignment fields
     red_reviewer_assignee: uuid.UUID | None = None
@@ -340,6 +346,8 @@ class TestOut(BaseModel):
     blue_review_by: uuid.UUID | None = None
     blue_review_at: datetime | None = None
     blue_review_notes: str | None = None
+    red_reviewer_assignee_username: str | None = None
+    blue_reviewer_assignee_username: str | None = None
     system_gaps: str | None = None
 
     # On-hold fields
@@ -398,6 +406,23 @@ class TestOut(BaseModel):
         except Exception:  # nosec B110
             pass  # DetachedInstanceError or similar — leave technique fields None
 
+        # Resolved assignee usernames (lazy-load, same as technique above).
+        # A plain operator/tech viewing their own test can't call
+        # GET /users/operators (lead/manager-only) to resolve an assignee ID
+        # into a name, so the API needs to hand it over pre-resolved.
+        for attr, field in (
+            ("red_tech_assigned_user", "red_tech_assignee_username"),
+            ("blue_tech_assigned_user", "blue_tech_assignee_username"),
+            ("red_reviewer", "red_reviewer_assignee_username"),
+            ("blue_reviewer", "blue_reviewer_assignee_username"),
+        ):
+            try:
+                user = getattr(obj, attr, None)
+                if user is not None:
+                    obj.__dict__[field] = user.username
+            except Exception:  # nosec B110
+                pass  # DetachedInstanceError or similar — leave username None
+
         # Only split evidences when they are already in memory (loaded via joinedload)
         raw_evs = obj.__dict__.get("evidences")
         if raw_evs is not None: