ci: pin sqlite3 + pre-fetch onnxruntime offline

Run 11 reached the build and revealed two issues:
- Runner re-resolved sqlite3 to 3.3.3 (cn mirror), mismatching the
  vendored 3.3.2 binary hash. Pin it via dependency_overrides.
- flutter_onnxruntime's github download of ONNX Runtime failed.
  Pre-fetch it via a China-accessible proxy into the plugin's
  expected build path so it skips the download and bundles the dll.

pubspec.yaml

@@ -51,6 +51,13 @@ dependencies:
   # Embedded ONNX runtime (local OCR recognition backend)
   flutter_onnxruntime: ^1.8.0
 
+# Pin sqlite3 to the exact version whose native binaries are vendored under
+# vendor/sqlite3/ (see hooks block below). Without this, pub re-resolves to the
+# latest sqlite3 on the cn mirror (e.g. 3.3.3), whose expected binary hash no
+# longer matches the vendored files and the native-asset build fails.
+dependency_overrides:
+  sqlite3: 3.3.2
+
 dev_dependencies:
   flutter_test:
     sdk: flutter