fix(dev): Register static assets without identifier for relative src paths

The staticAssetsMapper was only registering paths with the config key name
(e.g., 'assets'), which broke relative asset references like src='./cat.png'.

Changes:
1. Dev server: Register assets at both target/identifier/file and target/file
   so relative paths like src='./cat.png' resolve correctly
2. Deploy: Add destination: 'assets' to include_assets step so assets are
   copied to assets/ subdirectory with correct manifest paths

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

@@ -420,6 +420,8 @@ 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')
     })
   })
 
@@ -475,6 +477,8 @@ 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

@@ -253,6 +253,7 @@ async function staticAssetsMapper(
   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),