manager: start/restart at will, no approval; refuse self

new manager tools mcp__hyperhive__{start,restart} that delegate to the
existing lifecycle::start / lifecycle::restart on the host. kill was
already at the manager's discretion; rounding out start + restart for
parity so day-to-day container care doesn't have to round-trip through
the operator.

guard: refuse self-targeting on kill/start/restart — the manager would
just be cutting its own legs. spawn (request_spawn) and config changes
(request_apply_commit) still go through the approval queue, since those
are the actual gate. prompt + claude.md updated to make the boundary
explicit. kill now also emits HelperEvent::Killed (it didn't before).

hive-sh4re/src/lib.rs

@@ -267,6 +267,14 @@ pub enum ManagerRequest {
     Kill {
         name: String,
     },
+    /// Start a previously-stopped sub-agent container.
+    Start {
+        name: String,
+    },
+    /// Restart a sub-agent container (stop + start).
+    Restart {
+        name: String,
+    },
     /// Submit a config commit for the user to approve. `commit_ref` is opaque
     /// to the host (typically a git sha pointing into the agent's config repo).
     /// On approval the host applies the change via `nixos-container update`.