Fix sub-modal (ingredient) closing parent modal (recipe editor)

Problem: ingredient modal's closeModal called history.back(), which
triggered recipe editor's popHandler → closed recipe editor too.

Fix: modal suspend/resume system.
- When sub-modal opens, parent modal's popHandler is suspended
- When sub-modal closes, parent is resumed
- Parent popHandler ignores popstate events while suspended
- closeModal resumes parent before calling history.back()

Also: closeModal now pops exactly 1 history entry (not _historyDepth).
The _historyDepth counter tracks fullscreen entries within the modal,
which are handled by popHandler's decrements. closeModal only needs
to pop the modal's own base entry.

frontend/js/main.js

@@ -806,15 +806,21 @@ function showModal(html, onSubmit) {
         <button id="modal-ok" class="btn-primary">Сохранить</button>
       </div>
     </div>`;
+  // Suspend parent modal if sub-modal opening on top
+  const parentOverlay = document.querySelector(".modal-overlay");
+  if (parentOverlay && parentOverlay._suspend) parentOverlay._suspend();
+
   document.body.appendChild(overlay);
 
   // Simple history stack: each open = pushState, each back = popState pops it.
   // Modal = 1 entry. Fullscreen map/chart inside modal = 1 more entry each.
   // Back always pops the top entry. No re-pushing, no flags.
   let _historyDepth = 1; // how many entries this modal owns
+  let _suspended = false; // true when sub-modal is open on top
   history.pushState({ modal: true }, "");
 
   const popHandler = () => {
+    if (_suspended) return; // sub-modal handles this popstate
     _historyDepth--;
 
     // Check what's on top and collapse it
@@ -855,13 +861,19 @@ function showModal(html, onSubmit) {
     history.pushState({ modalFs: true }, "");
   };
 
+  // Suspend/resume this modal's popHandler when a sub-modal opens on top
+  overlay._suspend = function() { _suspended = true; };
+  overlay._resume = function() { _suspended = false; };
+
   function closeModal() {
     window.removeEventListener("popstate", popHandler);
     overlay.remove();
-    // Pop all entries this modal owns
-    if (_historyDepth > 0) {
-      for (let i = 0; i < _historyDepth; i++) history.back();
-    }
+    // Resume parent modal if this was a sub-modal
+    const parent = document.querySelector(".modal-overlay");
+    if (parent && parent._resume) parent._resume();
+    // Pop this modal's history entry
+    _modalPopHandled = true;
+    history.back();
   }
 
   overlay.querySelector("#modal-back").onclick = () => closeModal();