fix(dev): WP-37 — dev-switcher resets scenario/role instead of sticking

currentScenario()/currentRole() read the URL param before sessionStorage, so a
stale ?scenario=/?role= in the address bar overrode the switcher on reload
("stuck on slow"). The switcher now strips both dev params from the URL
(pure stripDevParams + history.replaceState) before reloading, so the stored
value wins.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/shared/infrastructure/dev-params.ts

@@ -0,0 +1,14 @@
+/**
+ * Remove the dev-only `?scenario=` and `?role=` params from a URL (WP-37). Once the
+ * dev switcher (debug-state) has been used, sessionStorage is the authoritative source
+ * for both — `currentScenario()`/`currentRole()` read the URL FIRST, so a stale param
+ * left in the address bar would override the switcher on reload (the "stuck on slow"
+ * bug). Stripping the params before reload lets the stored value win. Pure: returns the
+ * rewritten href, mutates nothing.
+ */
+export function stripDevParams(href: string): string {
+  const url = new URL(href);
+  url.searchParams.delete('scenario');
+  url.searchParams.delete('role');
+  return url.toString();
+}