Bump ai to a9eb685c1819b1cf45f0896280449cd6a1dd7171

Changes:
```
> git log --format="%C(auto) %h %s" ee5b2b2..a9eb685
 https://dart.googlesource.com/ai.git/+/a9eb685 add an example of using progress tokens to the tools example (270)
 https://dart.googlesource.com/ai.git/+/f167ace fix: Update README.md (268)
 https://dart.googlesource.com/ai.git/+/4c523d5 [dart_mcp_server] Update link of "Add to Cursor" button (265)

```

Diff: https://dart.googlesource.com/ai.git/+/ee5b2b25a013322307a60e445b480bc57ec34217..a9eb685c1819b1cf45f0896280449cd6a1dd7171/
Change-Id: Ifd3443c1af2f855acafff93962c540fa31d7463a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/446980
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Auto-Submit: Devon Carew <devoncarew@google.com>
diff --git a/DEPS b/DEPS
index 093175b..9ba9e63 100644
--- a/DEPS
+++ b/DEPS
@@ -131,7 +131,7 @@
   ### /third_party/pkg dependencies
   # 'tools/rev_sdk_deps.dart' will rev pkg dependencies to their latest; put an
   # EOL comment after a dependency to instead pin at the current revision.
-  "ai_rev": "ee5b2b25a013322307a60e445b480bc57ec34217",
+  "ai_rev": "a9eb685c1819b1cf45f0896280449cd6a1dd7171",
   "core_rev": "b59ecf4ceebe6153e1c0166b7c9a7fdd9458a89d",
   "dartdoc_rev": "82b48b53128a474221269a05a947bae28e2d7ac6",
   "ecosystem_rev": "68ff911b19e1abf00ff43b2b37bd16b1af01e088",