scheduling: clamp get_logs host-side, and fix two authorization claims

`docs/tools/scheduling.md` said three things about who may do what. Two
were wrong prose; the third was the code.

"All scheduling ops go through the operator approval queue" — one of the
five does. Cancel, edit, list and fire are `require_group("scheduling")`
and nothing else (socket_server/mod.rs:594-643), which is what the MCP
tool descriptions already tell an agent. The page pushed in the cautious
direction: someone watching a runaway recurring schedule would wait for
an operator rather than cancel it themselves.

The authorization sentence covered "read/cancel/edit". Cancel, edit and
fire really do check `cancel_authorized` (self, operator, or subtree) from
three call sites. `handle_list_schedules` takes no requester at all and
returns every row — now stated, along with the part that matters: the
snapshot includes other agents' schedule bodies.

`lines` was documented as "host-capped at 500" and the 500 was in the
agent's own MCP layer, not the host; `handle_get_logs` passed any u32
straight into JournalQuery. A limit in the caller is not a limit, so the
host clamps instead of the sentence changing. That also makes args.rs's
arg doc and the tool description agents read correct, untouched. The
sibling `get_host_journal` already clamps host-side at 100, which is both
the precedent and the control that the missing clamp here was real.

Closes #4230.

hive-c0re/src/socket_server/mod.rs

@@ -1121,7 +1121,10 @@ pub(crate) fn handle_send(
 /// `-M` read needs root). `journalctl -M` wants the `h-<name>` machine
 /// name, which `container_name` derives.
 async fn handle_get_logs(agent: &str, lines: Option<u32>) -> Response {
-    let n = lines.unwrap_or(50);
+    // Clamped here and not only in the MCP layer that also clamps it: a
+    // caller-side limit is not a limit, and anything speaking this socket
+    // sets `lines` itself. Mirrors `handle_get_host_journal`'s own cap.
+    let n = lines.unwrap_or(50).min(500);
     let machine = crate::lifecycle::container_name(agent);
     tracing::info!(%agent, %machine, %n, "manager: get_logs");
     match crate::priv_client::read_container_journal(