feat(studio): inline README + per-module update badge in Store (v0.19.0)

Two Phase-2 Store improvements that operators feel
immediately:

- Per-module update badge: store cards compare the operator's
  installed version against the index's `best_version`, raise
  an "update" pill + "Update to vX.Y.Z" button when newer is
  available. Result: a single glance at the Store reveals
  what's behind. The page now fetches `listModules` in
  parallel with the search so the comparison is on the
  current snapshot.

- Inline README rendering: detail sheet has a new
  Documentation section. "Load documentation" button (lazy —
  no network until clicked) calls FetchModuleDocs and renders
  the markdown via flutter_markdown, with the operator's
  theme colors and link-tap routed through SystemActions.
  Auth / not-found / network failures fall back to a
  friendly fix-hint panel + "Open repository in browser"
  button so the operator never hits a dead end.

Adds flutter_markdown ^0.7.7 to pubspec; the package is
maintenance-only upstream but is the only mature option
for Material-themed markdown right now. Easy to swap to
markdown_widget if/when we need GitHub-flavored extras.

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: "0.9.0"
+    version: "0.10.0"
   fake_async:
     dependency: transitive
     description:
@@ -125,6 +125,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.0.0"
+  flutter_markdown:
+    dependency: "direct main"
+    description:
+      name: flutter_markdown
+      sha256: "08fb8315236099ff8e90cb87bb2b935e0a724a3af1623000a9cec930468e0f27"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.7+1"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -279,6 +287,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.3.0"
+  markdown:
+    dependency: transitive
+    description:
+      name: markdown
+      sha256: ee85086ad7698b42522c6ad42fe195f1b9898e4d974a1af4576c1a3a176cada9
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.3.1"
   matcher:
     dependency: transitive
     description: