docs(snapshots): Clarify that context keys are automatically generated

Change wording from 'can generate' to 'automatically generates' to make
it clear that SnapshotPreviews always generates these context keys for
every preview, not conditionally.

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

Co-authored-by: Cameron Cooke <web@cameroncooke.com>

Author: cursoragent

docs/platforms/apple/common/snapshots/snapshotpreviews-metadata.mdx

@@ -86,7 +86,7 @@ SnapshotPreviews generates default sidecar metadata for each preview. The exact
 
 ## Generated Context Keys
 
-SnapshotPreviews can generate these `context` keys:
+SnapshotPreviews automatically generates these `context` keys:
 
 - `test_name`
 - `accessibility_enabled`