Auto-wrap desktop session tabs to a second row on overflow

When desktop session tabs overflow one row, wrap them to a second row instead
of horizontal scroll — unless the user has pinned the manual two-row layout
(tabTwoRows). Mobile/tablet keep horizontal scroll. The wrap policy
(shouldAutoWrapTabs) lives in constants.js as a pure, unit-testable function;
updateTabOverflowMode() measures overflow after each tab render and toggles
.tabs-auto-wrap.

Test: test/tab-overflow.test.ts (vm-loads constants.js, asserts the policy).

src/web/public/app.js

@@ -2656,6 +2656,39 @@ class CodemanApp {
       this._fullRenderSessionTabs();
     }
 
+    this.updateTabOverflowMode();
+  }
+
+  // Auto-wrap desktop session tabs to a second row when they overflow one row,
+  // unless the user has pinned the manual two-row layout (tabTwoRows). Mobile/
+  // tablet keep horizontal scroll. Policy lives in constants.js for unit testing.
+  updateTabOverflowMode() {
+    const container = this.$('sessionTabs');
+    if (!container) return;
+
+    const deviceType = MobileDetection.getDeviceType();
+    const settings = this.loadAppSettingsFromStorage();
+    const defaults = this.getDefaultSettings();
+    const manualTwoRows = deviceType === 'desktop' ? (settings.tabTwoRows ?? defaults.tabTwoRows ?? false) : false;
+
+    if (manualTwoRows || deviceType !== 'desktop') {
+      container.classList.remove('tabs-auto-wrap');
+      return;
+    }
+
+    // Measure the natural one-row overflow, then enable wrapping only if needed.
+    container.classList.remove('tabs-auto-wrap');
+    const shouldWrap = window.CodemanTabOverflow?.shouldAutoWrapTabs
+      ? window.CodemanTabOverflow.shouldAutoWrapTabs({
+          deviceType,
+          manualTwoRows,
+          tabCount: this.sessions.size,
+          scrollWidth: container.scrollWidth,
+          clientWidth: container.clientWidth,
+        })
+      : container.scrollWidth > container.clientWidth + 1;
+
+    container.classList.toggle('tabs-auto-wrap', shouldWrap);
   }
 
   _fullRenderSessionTabs() {