fix: keep dashboard shell dimensions stable

surfaces/shell/src/browser/HostApp.tsx

@@ -115,8 +115,10 @@ const shellStyles = {
   actions: { display: "flex", gap: designToken("spacing.sm"), justifyContent: "center" },
   aside: {
     borderRight: `${designToken("border.width")} solid ${designToken("border.divider")}`,
+    boxSizing: "border-box",
     minWidth: "13rem",
     padding: designToken("spacing.lg"),
+    width: "13rem",
   },
   groupLabel: {
     color: designToken("text.muted"),
@@ -140,10 +142,17 @@ const shellStyles = {
     color: designToken("text.primary"),
     display: "grid",
     fontFamily: designToken("typography.family-sans"),
-    gridTemplateColumns: "auto 1fr",
+    gridTemplateColumns: "13rem minmax(0, 1fr)",
     minHeight: "100vh",
+    minWidth: 0,
+    width: "100%",
+  },
+  main: {
+    boxSizing: "border-box",
+    minWidth: 0,
+    overflowX: "auto",
+    padding: designToken("spacing.lg"),
   },
-  main: { padding: designToken("spacing.lg") },
   message: {
     color: designToken("text.secondary"),
     display: "grid",
@@ -531,7 +540,7 @@ export function HostApp(props: HostAppProps): ReactElement {
   const { groups, ungrouped } = bootstrap.navigation;
 
   return (
-    <div style={shellStyles.layout}>
+    <div data-testid="host-shell" style={shellStyles.layout}>
       <header style={shellStyles.header}>
         <h1 style={shellStyles.heading}>Ekklesia</h1>
         <Button data-testid="host-logout" onClick={() => void signOut()}>

surfaces/shell/src/browser/ModuleUiFrame.tsx

@@ -116,7 +116,10 @@ export function ModuleUiFrame(props: ModuleUiFrameProps): ReactElement {
   }, [config, descriptor, importModule, onAuthorizationResponse, principal]);
 
   return (
-    <section aria-live="polite" style={{ display: "grid", gap: "0.75rem" }}>
+    <section
+      aria-live="polite"
+      style={{ display: "grid", gap: "0.75rem", minWidth: 0, width: "100%" }}
+    >
       {status === "loading" ? (
         <p data-testid="module-loading" style={{ color: "#57534e", margin: 0 }}>
           Loading module…
@@ -128,7 +131,7 @@ export function ModuleUiFrame(props: ModuleUiFrameProps): ReactElement {
           to check the installation.
         </p>
       ) : undefined}
-      <div data-testid="module-container" ref={containerRef} />
+      <div data-testid="module-container" ref={containerRef} style={{ minWidth: 0, width: "100%" }} />
     </section>
   );
 }