fix(web): keep the model quick-switch menu inside the viewport

The menu opens above its pill with a 160px minimum height, so a pill near the
top of the viewport produced a menu that reached past the viewport edge and
could not be scrolled to. Clamp the height to the space that is actually
available; the 360px cap is unchanged.

Author: elkaix

.changeset/web-model-dropdown-viewport.md

@@ -0,0 +1,5 @@
+---
+"@pymodel/pythinker-code": patch
+---
+
+Keep the web model quick-switch menu inside the viewport when the composer sits near the top of the window.

apps/pythinker-web/src/components/Composer.vue

@@ -749,7 +749,7 @@ function toggleDropdown(): void {
   if (dropdownOpen.value) {
     const rect = modelPillRef.value?.getBoundingClientRect();
     modelDropdownStyle.value = rect
-      ? { maxHeight: `${Math.min(360, Math.max(160, rect.top - 4 - 12))}px` }
+      ? { maxHeight: `${Math.min(360, Math.max(0, rect.top - 4 - 12))}px` }
       : {};
     permDropdownOpen.value = false;
     document.addEventListener('click', onDocClick, true);

apps/pythinker-web/test/composer.test.ts

@@ -408,9 +408,11 @@ describe('Composer model dropdown', () => {
     const pill = wrapper.get('.model-pill');
     const rect = vi.spyOn(pill.element, 'getBoundingClientRect');
 
+    // A pill near the top of the viewport used to get a 160px menu that reached
+    // above the viewport edge, so its upper entries could not be scrolled to.
     rect.mockReturnValue({ top: 20 } as DOMRect);
     await pill.trigger('click');
-    expect(wrapper.get('.model-dropdown').element.style.maxHeight).toBe('160px');
+    expect(wrapper.get('.model-dropdown').element.style.maxHeight).toBe('4px');
 
     rect.mockReturnValue({ top: 300 } as DOMRect);
     await pill.trigger('click');