fix: revert null-aware map entries; disable use_null_aware_elements lint

The ? operator on map entries applies to the key, not the value.
String literal keys can never be null, so ?'key': value was flagged as
invalid_null_aware_operator. Reverted to if (x != null) 'key': x form
and disabled the lint project-wide since it doesn't apply here.

analysis_options.yaml

@@ -23,6 +23,9 @@ linter:
   rules:
     # avoid_print: false  # Uncomment to disable the `avoid_print` rule
     # prefer_single_quotes: true  # Uncomment to enable the `prefer_single_quotes` rule
+    # ?'key': value applies ? to the key (never null for string literals);
+    # the if (x != null) form is correct for nullable-value map entries.
+    use_null_aware_elements: false
 
 # Additional information about this file can be found at
 # https://dart.dev/guides/language/analysis-options

lib/data/api/notes_api.dart

@@ -38,7 +38,7 @@ class NotesApi {
         'title': title,
         'body': body,
         'tags': tags,
-        ?'project_id': projectId,
+        if (projectId != null) 'project_id': projectId,
       });
       return Note.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {
@@ -59,7 +59,7 @@ class NotesApi {
         'title': title,
         'body': body,
         'tags': tags,
-        if (clearProject) 'project_id': null else ?'project_id': projectId,
+        if (clearProject) 'project_id': null else if (projectId != null) 'project_id': projectId,
       });
       return Note.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {

lib/data/api/projects_api.dart

@@ -44,7 +44,7 @@ class ProjectsApi {
         if (description != null && description.isNotEmpty)
           'description': description,
         if (goal != null && goal.isNotEmpty) 'goal': goal,
-        ?'color': color,
+        if (color != null) 'color': color,
       });
       return Project.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {

lib/data/api/tasks_api.dart

@@ -43,8 +43,8 @@ class TasksApi {
         'status': status.value,
         'priority': priority.value,
         'due_date': dueDate?.toIso8601String(),
-        ?'project_id': projectId,
-        ?'parent_id': parentId,
+        if (projectId != null) 'project_id': projectId,
+        if (parentId != null) 'parent_id': parentId,
       });
       return Task.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {