fix(bazel): ensure FTXUI is publicly accessible and add external smoke test (#1157)

- Set `visibility = ["//visibility:public"]` on the top-level `:ftxui` alias
  so the library can be consumed from external Bazel workspaces.
- Add `bazel_integration/` minimal external workspace to validate
  external usage via Bzlmod.
- Introduce `smoke` target that depends on `@ftxui//:ftxui`.
- Add CI job to build the smoke target using:
    --enable_bzlmod
    --override_module=ftxui=..
  This prevents regressions in visibility or public API changes.

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

.github/workflows/build.yaml

@@ -56,6 +56,13 @@ jobs:
           CXX: ${{ matrix.cxx }}
         run: bazel test --test_output=all ...
 
+      - name: "Bazel Smoke test"
+        env:
+          CC: ${{ matrix.cc }}
+          CXX: ${{ matrix.cxx }}
+        run: bazel build //... --enable_bzlmod --override_module=ftxui=../..
+        working-directory: bazel/test
+
   test_cmake:
     name: "CMake, ${{ matrix.compiler }}, ${{ matrix.os }}"
     strategy: