hivectl: add agent <name> watch to follow live events from the CLI

hivectl/src/cli.rs

@@ -534,6 +534,14 @@ pub enum AgentCmd {
         #[arg(long = "resume", value_name = "SESSION")]
         resume_session: Option<String>,
     },
+    /// Follow this agent's live turn/tool-call event stream from the CLI.
+    ///
+    /// Dials the same unix socket the gateway's nginx already proxies
+    /// through (no gateway hop, no daemon round-trip for the stream
+    /// itself) and prints one compact line per event. `Ctrl-C` to stop.
+    /// Requires the agent to be running (its harness must have bound the
+    /// web UI socket).
+    Watch,
     /// This agent's disk accounting + optional quota via btrfs qgroups.
     ///
     /// Needs `hivectl quota-enable` run once hive-wide first. No-op on