fix(#3344): type the roster entry's name as Ident, per review

A bare String in a crate whose whole suite types validated names as
hive_types::Ident, so a consumer had to re-derive at the boundary what every
sibling field gets checked for free.

Ident is strictly narrower than the store's charset — [a-z0-9-] against the
[A-Za-z0-9._-] the users database allows, because that file holds humans too.
Every agent name is a legal Ident by construction (creation parses one before
the job is queued), so the narrowing costs real agents nothing. What it does
mean is that a human hand-added to the agent group cannot be described as an
agent: the reader omits that row and logs it, rather than failing the whole
roster or quietly shrinking the answer.

The REQUEST keeps its String. That side carries what a caller asked for, and
validating it server-side is what lets a bad name be refused with a message
instead of failing to deserialise.

swarm-controller/src/auth.rs

@@ -77,9 +77,10 @@ impl AuthBridge {
     /// facts, and only one of them is a valid render.
     pub async fn list_agent_identities(&self) -> Result<Vec<String>> {
         match self.request(&BridgeRequest::ListAgentIdentities).await? {
-            BridgeResponse::Agents { agents } => {
-                Ok(agents.into_iter().map(|entry| entry.name).collect())
-            }
+            BridgeResponse::Agents { agents } => Ok(agents
+                .into_iter()
+                .map(|entry| entry.name.into_string())
+                .collect()),
             other => {
                 anyhow::bail!("swarm-authelia-bridge answered a roster request with {other:?}")
             }