qbzd: install the rustls process-level CryptoProvider

The rustls crypto provider was not installed for `qbzd`, which caused the
process to panic:

> thread 'tokio-rt-worker' (15737) panicked at [...]/rustls-0.23.37/src/crypto/mod.rs:249:14:
>
> Could not automatically determine the process-level CryptoProvider from
> Rustls crate features.
> Call CryptoProvider::install_default() before this point to select a
> provider manually, or make sure exactly one of the 'aws-lc-rs' and 'ring'
> features is enabled.
> See the documentation of the CryptoProvider type for more information.

The function `ensure_crypto_provider()` was defined in the `qbz-cast` crate
which is obviously not a dependency of `qbzd`.

This commit moves `ensure_crypto_provider()` to `qbz-app`, calls it from `qbzd`
and updates `qbz` accordingly.

crates/qbz-app/Cargo.toml

@@ -24,3 +24,6 @@ chrono = { workspace = true }
 md-5 = { workspace = true }
 base64 = { workspace = true }
 rand = "0.10"
+
+# TLS provider selection
+rustls = { version = "0.23", features = ["aws_lc_rs"] }