feat(doctor): update banner via HubAdmin.CheckUpdate (v0.9.0)

Doctor page now opens with a slim banner above the summary strip
in two cases: an actually newer version on the channel ("Update
available — v0.x.y", success-tone "new" pill, release-notes URL
when present) or the release host being unreachable
("Release host unreachable", neutral "offline" pill, with the
network reason). When local matches latest the banner stays
hidden — quiet UI is the right default.

Hooks into the existing parallel-fetch in `HubService.doctor` so
the new RPC adds zero latency to the page load.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

pubspec.lock

@@ -79,7 +79,7 @@ packages:
       path: "../fai_dart_sdk"
       relative: true
     source: path
-    version: "0.1.0"
+    version: "0.2.0"
   fake_async:
     dependency: transitive
     description: