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

[dskkato]

Summary

This PR fixes the Bazel build configuration to make FTXUI properly consumable from external workspaces using Bzlmod, and adds integration tests to prevent regressions.

Problem

The previous alias target for :ftxui did not properly re-export headers from the underlying modules (component, dom, screen), causing compilation failures when external projects tried to consume as @ftxui//:ftxui:

error: module //:smoke does not depend on a module exporting 'ftxui/dom/elements.hpp'

Solution

1. Replace alias with ftxui_cc_library

Changed the top-level :ftxui target from a simple alias to a ftxui_cc_library that explicitly re-exports all public headers using glob(["include/ftxui/**/*.hpp"]). This ensures downstream consumers can access all FTXUI headers through the single @ftxui//:ftxui dependency.

2. Add External Integration Test
   Created bazel_integration as a minimal external workspace that:

• Uses Bzlmod with bazel_dep(name = "ftxui")
• Overrides the dependency to test the local version
  Includes a smoke test that exercises all three modules
• Validates that @ftxui//:ftxui works as a single dependency

3. Add CI Validation
   Added a new CI job that builds the smoke test using:

bazel build //:smoke --enable_bzlmod --override_module=ftxui=..

This prevents future regressions in external visibility or API accessibility.

Testing

cd bazel_integration
bazel build //:smoke --enable_bzlmod --override_module=ftxui=..
./bazel-bin/smoke  # Successfully runs interactive UI

[ArthurSonzogni]

Thanks!