feat(intents): onscreen entity annotations + App Intents tests

- bookmarkOnscreen(_:) publishes the viewed bookmark as the on-screen
  entity (NSUserActivity.appEntityIdentifier) so Siri can resolve "this"
  / "summarize this one"; applied to the BrowserView sheets in
  BookmarksView and SearchView
- Add MarksTests (XCTest) covering entity mapping, EntityIdentifier,
  IntentRouter, and the real perform() of SearchMarksIntent and
  OpenBookmarkIntent; wired into the Marks scheme test phase

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

project.yml

@@ -26,6 +26,8 @@ schemes:
       config: Debug
     test:
       config: Debug
+      targets:
+        - MarksTests
     profile:
       config: Release
     analyze:
@@ -89,6 +91,18 @@ targets:
         SKIP_INSTALL: YES
         APPLICATION_EXTENSION_API_ONLY: YES
 
+  MarksTests:
+    type: bundle.unit-test
+    platform: iOS
+    sources:
+      - path: MarksTests
+    settings:
+      base:
+        PRODUCT_BUNDLE_IDENTIFIER: com.magicive.marks.MarksTests
+        GENERATE_INFOPLIST_FILE: YES
+    dependencies:
+      - target: Marks
+
   MarksWidget:
     type: app-extension
     platform: iOS