fix(maestro): restore sidebar fill, pane title, and focus dimming after React port

The React port replaced CSS class names with Tailwind utilities, breaking
three visual contracts:

- SessionCard used inline bg-* classes instead of .is-active/.is-open/
  .is-previewing that the styles.css cascade targets.
- PaneTitle used className "at-title" instead of "attach-title", so font,
  overflow, and child layout rules never applied.
- MultiView's Pane never applied .is-focused or .is-preview, so every
  pane matched :not(.is-focused) and was dimmed to 0.45 opacity.

Closes #256

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/components/layout/MultiView.test.tsx

@@ -105,7 +105,7 @@ describe("MultiView", () => {
       expect(screen.getByText("Tab 1 · 1")).toBeTruthy();
       const pane = document.querySelector('[data-session-id="s9"]');
       expect(pane).toBeTruthy();
-      expect(pane!.querySelector(".bg-preview-tint")).toBeTruthy();
+      expect(pane!.classList.contains("is-preview")).toBe(true);
       expect(screen.getByText("preview")).toBeTruthy();
     });
 

web/src/components/layout/MultiView.tsx

@@ -188,8 +188,9 @@ function Pane({
   return (
     <div
       className={
-        "mv-pane flex h-full min-h-0 min-w-0 flex-col border " +
-        (isFocused && !isPreview ? "border-accent" : "border-border-strong")
+        "mv-pane flex h-full min-h-0 min-w-0 flex-col" +
+        (isFocused ? " is-focused" : "") +
+        (isPreview ? " is-preview" : "")
       }
       data-leaf-id={leaf.id}
       data-session-id={leaf.sessionId ?? undefined}
@@ -201,10 +202,7 @@ function Pane({
       }}
     >
       <div
-        className={
-          "mv-pane-header flex items-center justify-between gap-sp-2 border-b border-border-strong px-sp-2 py-sp-1 text-fs-12 " +
-          (isPreview ? "bg-preview-tint text-preview" : "bg-surface")
-        }
+        className="mv-pane-header attach-header flex items-center justify-between gap-sp-2 border-b border-border-strong px-sp-2 py-sp-1 text-fs-12"
       >
         {leaf.sessionId ? (
           <PaneTitle sessionId={leaf.sessionId} session={session} />

web/src/components/layout/PaneTitle.tsx

@@ -15,7 +15,7 @@ export interface PaneTitleProps {
 export function PaneTitle({ sessionId, session, className }: PaneTitleProps) {
   if (!session) {
     return (
-      <span className={className ?? "at-title"} title={sessionId}>
+      <span className={className ?? "attach-title"} title={sessionId}>
         session <span className="sid">{sessionId.slice(0, 8)}</span>
       </span>
     );
@@ -27,7 +27,7 @@ export function PaneTitle({ sessionId, session, className }: PaneTitleProps) {
   const icon = tool ? toolIconSvg(tool) : null;
 
   return (
-    <span className={className ?? "at-title"} title={`${name} · ${session.command}  (${sessionId})`}>
+    <span className={className ?? "attach-title"} title={`${name} · ${session.command}  (${sessionId})`}>
       <span className="at-name">{name}</span>
       {showCommand && (
         <span className="at-cmd">

web/src/components/sidebar/SessionCard.tsx

@@ -44,14 +44,17 @@ export interface SessionCardProps {
   onRenameCancel(): void;
 }
 
-/** The fill ladder from docs/SIDEBAR.md "Which row is filled", furthest down
- * wins. Written as one ordered run so the precedence is the order it reads in. */
-function rowFill(p: SessionCardProps): string {
-  if (p.active) return "bg-accent-fill";
-  if (p.previewing) return "bg-preview-tint";
-  if (p.open) return "bg-accent/[0.06]";
-  if (p.highlighted) return "bg-preview-tint";
-  return "";
+/** The fill ladder from docs/SIDEBAR.md "Which row is filled" — the CSS
+ * cascade in styles.css carries the actual fills via `.is-active`, `.is-open`,
+ * `.is-previewing` (all inside `:where()` so source order is the precedence).
+ * We just apply the right class names here. */
+function rowClasses(p: SessionCardProps): string {
+  const cls: string[] = [];
+  if (p.active) cls.push("is-active");
+  if (p.open) cls.push("is-open");
+  if (p.previewing) cls.push("is-previewing");
+  if (p.highlighted) cls.push("is-highlighted");
+  return cls.join(" ");
 }
 
 export function SessionCard(props: SessionCardProps) {
@@ -62,7 +65,7 @@ export function SessionCard(props: SessionCardProps) {
 
   return (
     <a
-      className={`session-card tree-leaf no-underline ${rowFill(props)} ${
+      className={`session-card tree-leaf no-underline ${rowClasses(props)} ${
         running ? "" : "opacity-60"
       }`}
       href={`#/attach/${encodeURIComponent(s.id)}`}