build: add silero-coreml submodule (#19)

* build: add silero-coreml as git submodule

Replaces sibling-directory local package with in-repo submodule.
Updates Xcode relative paths and CI checkout to fetch submodules.

* build: add silero-coreml submodule

.github/workflows/ci.yml

@@ -118,16 +118,18 @@ jobs:
       - uses: subosito/flutter-action@v2
         with:
           channel: stable
+      - name: Try to fetch local SileroCoreML package
+        run: git submodule update --init --depth=1 silero-coreml || true
       - name: flutter pub get
         working-directory: apps/chanora_flutter
         run: flutter pub get
       - name: Check local SileroCoreML package
         id: silero-coreml
         run: |
-          if [ -d ../silero-coreml ]; then
+          if [ -f silero-coreml/Package.swift ]; then
             echo "available=true" >> "$GITHUB_OUTPUT"
           else
-            echo "::notice::Skipping iOS build because ../silero-coreml is not available on this runner"
+            echo "::notice::Skipping iOS build because silero-coreml submodule is not available"
             echo "available=false" >> "$GITHUB_OUTPUT"
           fi
       - name: flutter build ios --no-codesign