swarm-ui: move the shell's route layout predicates out and test them

isFullBleedRoute and isWideBodyRoute are plain functions of a path, so
they move from Shell.tsx to shell/routes.ts, where the new tests cover
the start page, the hive directory's move to /hives, the terminal
paths and the wide-body routes.

frontend/packages/swarm-ui/src/shell/routes.ts

@@ -0,0 +1,35 @@
+// Which layout a route gets inside the shell: the readable-width cap, the
+// wide body, or full-bleed. Kept apart from `Shell.tsx` so it is plain
+// functions of a path, with no DOM or CSS behind it, and can be tested.
+
+// Routes that opt out of `.shell-body`'s 60em readable-line-length cap
+// — mara screenshotted the issue report's 8-column table getting
+// clipped; that width is deliberate for the rest of the UI's cards/
+// forms, but too narrow for a wide table. `.shell-body-wide` (Shell.css) is a
+// modifier alongside the base class, not a replacement, so every other
+// route's layout is untouched. `/agents` joined for the same reason —
+// its own table view (plus the list+detail split) hits the same cap.
+const WIDE_BODY_ROUTES = new Set([
+  "/issues",
+  "/agents",
+  "/review-runs",
+  "/review-tryout",
+]);
+
+// `/agents/:name/terminal` (and a subagent's, under
+// `/agents/:name/subagents/:subagent/`) is full-bleed: the terminal fills
+// the whole viewport below the header bar, edge to edge (`shell-full` /
+// `shell-body-full` in Shell.css). It can't join the `Set` above — it's a
+// parameterized path, one literal string can't match every agent name.
+const FULL_BLEED_ROUTE_PATTERN =
+  /^\/agents\/[^/]+(\/subagents\/[^/]+)?\/terminal$/;
+
+// The start page (`/`) is full-bleed too: its rain backdrop fills the whole
+// body below the header.
+export function isFullBleedRoute(location: string): boolean {
+  return location === "/" || FULL_BLEED_ROUTE_PATTERN.test(location);
+}
+
+export function isWideBodyRoute(location: string): boolean {
+  return WIDE_BODY_ROUTES.has(location);
+}