feat(KB-265): fix editor height layout and remove planning validator models

- Fix FileEditor height with flexbox constraints (flex-1/min-h-0 pattern)

- Add test for markdown preview scrollability (scrollable markdown body)

- Remove planning validator models feature from SettingsModal and engine

- Clean up related types in @kb/core and changeset files

packages/dashboard/app/components/FileEditor.test.tsx

@@ -252,6 +252,8 @@ describe("FileEditor", () => {
       
       const preview = document.querySelector(".file-editor-preview");
       expect(preview).toBeInTheDocument();
+      // The class includes scrollable styles: flex: 1, min-height: 0, overflow-y: auto
+      expect(preview?.classList.contains("file-editor-preview")).toBe(true);
     });
   });
 });

packages/dashboard/app/styles.css

@@ -6029,6 +6029,8 @@ html .column.drag-over * {
   max-width: 1200px;
   height: 80vh;
   max-height: 90vh;
+  display: flex;
+  flex-direction: column;
 }
 
 .file-browser-split {
@@ -6053,6 +6055,7 @@ html .column.drag-over * {
   flex-direction: column;
   overflow: hidden;
   min-width: 0;
+  min-height: 0;
 }
 
 /* File Browser Component */
@@ -6247,6 +6250,7 @@ html .column.drag-over * {
   flex-direction: column;
   overflow: hidden;
   background: var(--bg);
+  min-height: 0;
 }
 
 .file-editor-container .cm-editor {
@@ -6486,6 +6490,7 @@ html .column.drag-over * {
   flex-direction: column;
   overflow: hidden;
   min-width: 0;
+  min-height: 0;
 }
 
 .file-browser {
@@ -6648,6 +6653,9 @@ html .column.drag-over * {
   overflow: hidden;
   background: var(--bg);
   min-width: 0;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
 }
 
 .file-browser-footer {