ironhtml-bootstrap: v5 feature flag does nothing

[dannywillems]

Description

`crates/ironhtml-bootstrap/Cargo.toml:22-23` declares a `v5` feature as the default:

```toml
[features]
default = ["v5"]
v5 = []
```

But there are no `#[cfg(feature = "v5")]` gates anywhere in the crate. The feature exists but is never checked.

Should either be removed or used to gate version-specific behavior.