feat(#1897): auto-fill the hive domain in peer-config (drop required --domain)

Per operator review: hivectl shouldn't make the operator retype this
hive's own domain. Add a HostRequest::HiveDomain admin-socket query
(c0re answers from HYPERHIVE_HIVE_DOMAIN, already in its service env) and
a domain field on HostResponse.

hivectl peer-config now resolves the domain as: --domain override (kept
for offline/scripted use), else the daemon query; errors with a clear
hint when neither resolves. wg init resolves it best-effort too, so it
prints the hand-over peer-config block without --domain (skipped, not
failed, when the daemon is unreachable).

Regenerated docs/tools/hivectl-cli.md.

hive-sh4re/src/lib.rs

@@ -44,6 +44,11 @@ pub enum HostRequest {
     Rebuild { name: String },
     /// List managed containers.
     List,
+    /// Report this hive's canonical DNS domain
+    /// (`services.hyperhive.domain`), or `None` when unset. Lets the
+    /// operator CLI fill in the hive's own identity (e.g. the federation
+    /// peer-config block) without the operator retyping it.
+    HiveDomain,
     /// List pending approval requests.
     Pending,
     /// Approve a pending request by id; the action runs immediately.
@@ -131,6 +136,10 @@ pub struct HostResponse {
     pub agents: Option<Vec<String>>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub approvals: Option<Vec<Approval>>,
+    /// This hive's canonical DNS domain — `HiveDomain` result. `None`
+    /// when the domain is unset (no `services.hyperhive.domain`).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub domain: Option<String>,
 }
 
 /// One row in the approval queue. `commit_ref` is overloaded per
@@ -218,6 +227,7 @@ impl HostResponse {
             error: None,
             agents: None,
             approvals: None,
+            domain: None,
         }
     }
 
@@ -228,6 +238,7 @@ impl HostResponse {
             error: Some(message.into()),
             agents: None,
             approvals: None,
+            domain: None,
         }
     }
 
@@ -238,6 +249,7 @@ impl HostResponse {
             error: None,
             agents: Some(agents),
             approvals: None,
+            domain: None,
         }
     }
 
@@ -248,6 +260,19 @@ impl HostResponse {
             error: None,
             agents: None,
             approvals: Some(approvals),
+            domain: None,
+        }
+    }
+
+    /// `HiveDomain` result — this hive's canonical domain (or `None`).
+    #[must_use]
+    pub fn hive_domain(domain: Option<String>) -> Self {
+        Self {
+            ok: true,
+            error: None,
+            agents: None,
+            approvals: None,
+            domain,
         }
     }
 }