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/Root.tsx

@@ -26,7 +26,6 @@ import { useTodos } from "./hooks/useTodos.js";
 import { fmtAge, fmtTokens } from "./lib/format.js";
 import { resolveDashboardBase } from "./lib/dashboardBase.js";
 import { submitPauseResume } from "./lib/pauseAction.js";
-import { postEffort } from "./lib/modelEffort.js";
 import {
   postCancelTurn,
   postLogout,
@@ -220,9 +219,6 @@ export function Root() {
               statusLabel="… connecting"
               statusTone="neutral"
               model=""
-              effort=""
-              availableEfforts={[]}
-              onSelectEffort={() => {}}
               paused={false}
               onTogglePause={() => {}}
               thinking={false}
@@ -308,10 +304,7 @@ export function Root() {
             resolvedModel={state.resolved_model ?? undefined}
             modelSource={state.model_source}
             effort={state.effort}
-            availableEfforts={state.available_efforts}
-            onSelectEffort={(level) => {
-              postEffort(level).then(() => refresh());
-            }}
+            effortSource={state.effort_source}
             ctxLabel={ctx !== null ? fmtTokens(ctx) : undefined}
             costLabel={cost !== null ? fmtTokens(cost) : undefined}
             paused={state.paused}