feat: preserve scroll position across case-action redirects

Clicking close/reopen or any bulk form submits a POST and follows the
303 to the listing, which is a fresh navigation — browsers do not
restore scroll on navigation, only on reload(). A user scrolled to
row 30 of a long list loses focus and has to scroll back manually.

Fix: small JS on my_cases.html that stashes window.scrollY in
sessionStorage before every form submit and restores it on the next
page load. Silent no-op when sessionStorage is blocked (strict
privacy mode), so the feature is purely additive.

No server changes — kept the redirect URLs clean. An earlier iteration
with a #case-<uuid> anchor on the redirect turned out to race with
the explicit scrollTo on any page where the referer scrollY was near
0; dropping the anchor made the JS the sole source of truth.

server/templates/my_cases.html

@@ -160,6 +160,38 @@ try {
   });
 })();
 
+// Preserve scroll position across POST-redirects (close, reopen,
+// bulk-*). Browsers keep scroll on location.reload() but NOT on a
+// redirect-driven navigation, even when the target URL matches the
+// referer. Without this, clicking close on row 30 of a long list
+// dumps the user back at scrollY=0 with the action-row off-screen.
+//
+// Mechanism: capture scrollY in sessionStorage before every form
+// submit on this page, restore it on the very next load, then delete.
+// Using the classic two-arg scrollTo(0, y) form — the options-object
+// variant is silently ignored in some older browsers.
+(() => {
+  const STASH = 'doctate:scrollY';
+  try {
+    document.querySelectorAll('form').forEach((f) => {
+      f.addEventListener('submit', () => {
+        sessionStorage.setItem(STASH, String(window.scrollY));
+      });
+    });
+    const stashed = sessionStorage.getItem(STASH);
+    if (stashed !== null) {
+      sessionStorage.removeItem(STASH);
+      const y = parseInt(stashed, 10);
+      if (!isNaN(y)) {
+        window.scrollTo(0, y);
+      }
+    }
+  } catch (_) {
+    // sessionStorage may be blocked (strict privacy mode) — silent fail,
+    // scroll returns to 0 like it did before this feature.
+  }
+})();
+
 // Live-update bus: any case event for this user triggers a debounced
 // page reload. Debounce collapses event bursts (e.g. bulk-delete) into
 // one reload. EventSource auto-reconnects on network drops.