fix(KB-660): fix Git Manager dialog rendering off-screen on small viewports

- Fix .gm-content min-height from 400px to 0 for proper flex behavior
- Add mobile responsive styles to prevent modal overflow
- Create changeset for patch release

packages/dashboard/app/styles.css

@@ -10562,6 +10562,9 @@ html .column.drag-over * {
   width: 900px;
   max-width: 95vw;
   max-height: 85vh;
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
 }
 
 /* Main layout: sidebar + content */
@@ -10627,7 +10630,7 @@ html .column.drag-over * {
   flex: 1;
   overflow-y: auto;
   padding: var(--space-lg);
-  min-height: 400px;
+  min-height: 0;
   position: relative;
 }
 
@@ -11659,7 +11662,7 @@ html .column.drag-over * {
   .gm-modal {
     width: 100%;
     max-width: 100%;
-    max-height: 100vh;
+    height: 100vh;
     border-radius: 0;
   }
 
@@ -11696,7 +11699,7 @@ html .column.drag-over * {
   }
 
   .gm-content {
-    min-height: 300px;
+    min-height: 200px;
     padding: var(--space-md);
   }