refactor(oauth-client): rename interactive/mod.rs to interactive.rs per CLAUDE.md
CLAUDE.md explicitly says: "No mod.rs. Use the foo.rs + foo/ sibling-file layout."
Renamed src/commands/test/oauth/client/pipeline/interactive/mod.rs to
interactive.rs so the file sits alongside the interactive/ directory.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>