agents: remove the hive-level /effort control too

mara on #5034: "effort shares /models fate". The per-agent web UI no
longer sets effort: the `/effort` slash command, the effort picker,
`POST /api/effort`, `Bus::set_effort`, the `hyperhive-effort` writer,
`EFFORT_LEVELS`/`is_valid_effort` and the ACP effort-list payload are
gone, and `lib/modelEffort.ts` with them. The effort chip is
display-only and shows its source (`effort_source` in `/api/state`);
on ACP it stays hidden while the session offers no effort level.

The read side is unchanged: with no swarm value an agent runs an
existing `hyperhive-effort` file, else its agent.nix effort, else
medium. Existing files are not touched.

Refs #5034

frontend/packages/agent/src/components/TermInput.tsx

@@ -11,7 +11,6 @@
 // (a local note explains what confirming does), typing it again within
 // the same "armed" state fires it — a keyboard-native two-step confirm.
 import { useRef, useState } from "preact/hooks";
-import { postEffort } from "../lib/modelEffort.js";
 import {
   postCancelTurn,
   postCompact,
@@ -32,10 +31,6 @@ const SLASH_COMMANDS: { name: string; desc: string }[] = [
   { name: "/clear", desc: "wipe the terminal panel (local-only)" },
   { name: "/cancel", desc: "SIGINT the in-flight claude turn" },
   { name: "/compact", desc: "compact the persistent claude session" },
-  {
-    name: "/effort",
-    desc: "/effort <level>  — set claude effort (medium/high/xhigh) for future turns",
-  },
   {
     name: "/new-session",
     desc: "fresh claude session next turn (type twice to confirm)",
@@ -80,8 +75,7 @@ export function TermInput({
 
   function handleSlash(line: string): boolean {
     const trimmed = line.trim();
-    const [cmd, ...rest] = trimmed.split(/\s+/);
-    const arg = rest.join(" ");
+    const [cmd] = trimmed.split(/\s+/);
     const wasArmed = armedRef.current === cmd;
     armedRef.current = null;
 
@@ -127,16 +121,6 @@ export function TermInput({
           );
         }
         return true;
-      case "/effort":
-        if (!arg)
-          onLocalNote(
-            "✗ /effort needs a level (e.g. /effort medium, /effort high, /effort xhigh)",
-          );
-        else
-          postEffort(arg).then(
-            (r) => !r.ok && reportFailure("/effort", r.detail),
-          );
-        return true;
       default:
         onLocalNote(`✗ unknown slash command: ${cmd} — try /help`);
         return true;