fix(dev): Register static assets at target path for relative src paths

Static assets were registered at target/identifier/file (e.g., target/assets/file),
but relative paths like src='./cat.png' resolve to target/file.

Changes:
1. Dev server: Register assets at target/file instead of target/identifier/file
2. Deploy: Add destination: 'assets' so assets copy to assets/ subdirectory

Fixes #5285

Author: MitchLillie

packages/app/src/cli/models/extensions/specifications/ui_extension.ts

@@ -113,6 +113,7 @@ const uiExtensionSpec = createExtensionSpecification({
                 anchor: 'extension_points[]',
                 groupBy: 'target',
                 key: 'extension_points[].assets',
+                destination: 'assets',
               },
               {
                 type: 'configKey',

packages/app/src/cli/services/dev/extension/payload.test.ts

@@ -418,8 +418,8 @@ describe('getUIExtensionPayload', () => {
           },
         },
       ])
-      expect(resolver.get('CUSTOM_EXTENSION_POINT/assets/foo.json')).toBe('foo.json')
-      expect(resolver.get('CUSTOM_EXTENSION_POINT/assets/subdir/bar.png')).toBe('subdir/bar.png')
+      expect(resolver.get('CUSTOM_EXTENSION_POINT/foo.json')).toBe('foo.json')
+      expect(resolver.get('CUSTOM_EXTENSION_POINT/subdir/bar.png')).toBe('subdir/bar.png')
     })
   })
 
@@ -473,8 +473,8 @@ describe('getUIExtensionPayload', () => {
         },
       ])
       // Both targets' resolver entries point at the same output-relative file.
-      expect(resolver.get('TARGET_A/assets/foo.json')).toBe('foo.json')
-      expect(resolver.get('TARGET_B/assets/foo.json')).toBe('foo.json')
+      expect(resolver.get('TARGET_A/foo.json')).toBe('foo.json')
+      expect(resolver.get('TARGET_B/foo.json')).toBe('foo.json')
     })
   })
 

packages/app/src/cli/services/dev/extension/payload.ts

@@ -252,7 +252,7 @@ async function staticAssetsMapper(
   if (files.length === 0) return {}
   const urlSubpath = `${target}/${identifier}`
   for (const file of files) {
-    resolver?.set(`${urlSubpath}/${file}`, file)
+    resolver?.set(`${target}/${file}`, file)
   }
   const updatedTimestamps = await Promise.all(
     files.map(async (file) => (await fileLastUpdatedTimestamp(joinPath(buildDirectory, file))) ?? 0),