Remove NavItemBlueprint in favor of page-based nav discovery

Drop the deprecated NavItemBlueprint from the public API and migrate core
plugins to set title and icon on PageBlueprint instead. AppNav keeps
backward compatibility for legacy nav-item extensions via an internal
core.nav-item.target data ref.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

app-config.yaml

@@ -63,13 +63,6 @@ app:
     # - apis.plugin.graphiql.browse.gitlab: true
     # - graphiql-endpoint:graphiql/gitlab: true
 
-    - nav-item:search: false
-    - nav-item:user-settings: false
-    - nav-item:catalog
-    - nav-item:api-docs
-    - nav-item:scaffolder
-    - nav-item:app-visualizer
-
     # Opt in to the experimental BUI scaffolder form theme
     - sub-page:scaffolder/templates:
         config: