swarm-ui: shared code leaves page folders; SectionHeading and Preformatted replace per-page copies

durationLabel moves to util.ts, termPaths to agent/terminal/term-paths.ts,
StateBadges and tokenTotal to agent/state, and TryOutResult to
pages/review-common, so the builds, runs and agent pages no longer import
across page folders. SectionHeading is the body-size section heading the
create form and the egress card each styled; Preformatted is the scrolling
text block of the builds tail and the AGENTS.md view, which now share one
chrome and are both keyboard-scrollable. The components page shows both.

frontend/packages/swarm-ui/test/tidy-helpers.test.mjs

@@ -0,0 +1,26 @@
+// Two helpers that used to live in page folders: how long a run took, and the
+// paths one terminal is reached at.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { durationLabel } from "../src/util.ts";
+import { termPaths } from "../src/agent/terminal/term-paths.ts";
+
+test("durationLabel names seconds, minutes and hours", () => {
+  assert.equal(durationLabel(0, 45), "45s");
+  assert.equal(durationLabel(0, 192), "3m 12s");
+  assert.equal(durationLabel(0, 3840), "1h 4m");
+});
+
+test("durationLabel reads a clock that ran backwards as 0s", () => {
+  assert.equal(durationLabel(100, 90), "0s");
+});
+
+test("an agent's terminal has a turn-state stream, a subagent's has none", () => {
+  const agent = termPaths("iris");
+  assert.equal(agent.page, "/agents/iris/terminal");
+  assert.equal(agent.state, "/api/agents/iris/state/stream");
+  const sub = termPaths("iris", "t 1");
+  assert.equal(sub.label, "iris/t 1");
+  assert.equal(sub.page, "/agents/iris/subagents/t%201/terminal");
+  assert.equal(sub.state, null);
+});