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/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

@@ -250,9 +250,8 @@ async function staticAssetsMapper(
   files: string[],
 ): Promise<Partial<DevNewExtensionPointSchema>> {
   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),
@@ -261,7 +260,7 @@ async function staticAssetsMapper(
     assets: {
       [identifier]: {
         name: identifier,
-        url: `${url}/assets/${urlSubpath}/`,
+        url: `${url}/assets/${target}/`,
         lastUpdated: Math.max(...updatedTimestamps),
       },
     },