fix: sidebar-item flex-shrink:0 — cards were compressing to fit, eliminating scroll

Without flex-shrink:0, flex compresses all sidebar cards proportionally
when the container is shorter than their total height. Cards visually
fit the screen with no overflow — scrollTop stays 0, touch handler
has nothing to scroll. One property restores the intended overflow.

muxplex/frontend/style.css

@@ -469,6 +469,7 @@ body {
 
 .sidebar-item {
   height: 120px;
+  flex-shrink: 0;          /* prevent flex from compressing cards to fit */
   background: var(--bg-secondary);
   cursor: pointer;
   overflow: hidden;

muxplex/tests/test_frontend_css.py

@@ -604,3 +604,12 @@ def test_sidebar_list_has_touch_action_pan_y():
     assert "overscroll-behavior: contain" in block, (
         ".sidebar-list must have overscroll-behavior:contain to prevent scroll chaining"
     )
+
+
+def test_sidebar_item_has_flex_shrink_zero():
+    """Regression: without flex-shrink:0 cards shrink to fit, eliminating scroll overflow."""
+    css = read_css()
+    block = _extract_rule_block(css, ".sidebar-item {")
+    assert "flex-shrink: 0" in block, (
+        ".sidebar-item must have flex-shrink:0 to prevent compression"
+    )