tighter schema for project brand

we don't allow brand metadata in projects
this only fixes project in _quarto.yml not root

Author: gordonwoodhull

src/resources/schema/definitions.yml

@@ -3343,6 +3343,17 @@
       defaults:
         ref: brand-defaults
 
+- id: brand-path-only-light-dark
+  anyOf:
+    - string
+    - object:
+        closed: true
+        properties:
+          light: string
+          dark: string
+  description: |
+    A path to a brand.yml file, or an object with light and dark paths to brand.yml
+
 - id: brand-path-bool-light-dark
   anyOf:
     - string # a file path

src/resources/schema/project.yml

@@ -34,11 +34,9 @@
             description: "Additional file resources to be copied to output directory"
         brand:
           schema:
-            ref: brand-path-bool-light-dark
+            ref: brand-path-only-light-dark
           description: |
-            Branding information to use for this document. If a string, the path to a brand file.
-            If false, don't use branding on this document. If an object, an inline brand
-            definition, or an object with light and dark brand paths or definitions.
+            Path to brand.yml or object with light and dark paths to brand.yml
         preview:
           description: Options for `quarto preview`
           schema: