fix(ui): align theme toggle with dashboard style

src/App.test.tsx

@@ -34,8 +34,11 @@ describe("React app dashboard state view", () => {
     );
 
     expect(html).toContain('data-ui-theme-toggle="true"');
+    expect(html).toContain('data-ui-theme-current="dark"');
     expect(html).toContain('aria-label="Switch to light theme"');
     expect(html).not.toContain("aria-pressed");
+    expect(html).toContain("Theme");
     expect(html).toContain("Dark");
+    expect(html).toContain("Light");
   });
 });

src/lib/ui/components/ThemeToggle.tsx

@@ -15,15 +15,22 @@ export function ThemeToggle({ theme, onThemeChange }: ThemeToggleProps) {
     <button
       aria-label={label}
       className="theme-toggle"
+      data-ui-theme-current={theme}
       data-ui-theme-toggle="true"
       onClick={() => onThemeChange(nextTheme)}
       type="button"
     >
-      <IconGlyph
-        name={theme === "dark" ? "mdi:weather-night" : "mdi:white-balance-sunny"}
-        size="sm"
-      />
-      <span>{theme === "dark" ? "Dark" : "Light"}</span>
+      <span className="theme-toggle__label">Theme</span>
+      <span className="theme-toggle__switch" aria-hidden="true">
+        <span className="theme-toggle__cell" data-active={theme === "dark"}>
+          <IconGlyph name="mdi:weather-night" size="sm" />
+          <span>Dark</span>
+        </span>
+        <span className="theme-toggle__cell" data-active={theme === "light"}>
+          <IconGlyph name="mdi:white-balance-sunny" size="sm" />
+          <span>Light</span>
+        </span>
+      </span>
     </button>
   );
 }

src/lib/ui/components/render.test.tsx

@@ -6,6 +6,7 @@ import { FooterCell } from "./FooterCell";
 import { IconButton } from "./IconButton";
 import { ServiceRow } from "./ServiceRow";
 import { TelemetryCard } from "./TelemetryCard";
+import { ThemeToggle } from "./ThemeToggle";
 import { dashboardPreviewFixtures } from "../fixtures";
 
 describe("dashboard UI components", () => {
@@ -144,4 +145,20 @@ describe("dashboard UI components", () => {
     expect(iconButton).toContain("class=\"icon-button custom-icon-action ");
     expect(iconButton).toContain("aria-expanded=\"false\"");
   });
+
+  test("renders the theme toggle as a segmented instrument control", () => {
+    const body = renderToString(
+      <ThemeToggle theme="light" onThemeChange={() => undefined} />,
+    );
+
+    expect(body).toContain('class="theme-toggle"');
+    expect(body).toContain('data-ui-theme-current="light"');
+    expect(body).toContain('aria-label="Switch to dark theme"');
+    expect(body).toContain('class="theme-toggle__label"');
+    expect(body).toContain('class="theme-toggle__switch"');
+    expect(body).toContain('data-active="true"');
+    expect(body).toContain("Theme");
+    expect(body).toContain("Dark");
+    expect(body).toContain("Light");
+  });
 });

src/lib/ui/components/styles.css

@@ -565,35 +565,90 @@
 }
 
 .theme-toggle {
-  display: inline-grid;
-  grid-auto-flow: column;
-  gap: var(--ui-space-2);
+  display: grid;
+  grid-template-columns: 2.72rem minmax(0, 1fr);
   align-items: center;
-  justify-content: center;
-  min-width: 6.5rem;
-  min-height: 2.15rem;
-  border: var(--ui-border);
-  background: var(--ui-color-surface-raised);
+  width: 9.75rem;
+  min-width: 0;
+  min-height: 2.18rem;
+  border: var(--ui-border-strong);
+  background: var(--ui-color-surface-module);
   color: var(--ui-color-text);
   cursor: pointer;
   font: inherit;
-  font-size: 0.62rem;
+  font-size: 0.55rem;
   font-weight: 850;
   letter-spacing: 0;
-  padding: 0 var(--ui-space-3);
+  padding: 0.13rem;
   text-transform: uppercase;
+  box-shadow: var(--ui-shadow-hard);
 }
 
 .theme-toggle:hover {
   border-color: var(--ui-color-accent);
-  color: var(--ui-color-accent);
 }
 
-.theme-toggle span {
+.theme-toggle__label {
+  display: grid;
+  align-self: stretch;
+  place-items: center;
+  border-right: var(--ui-border);
+  color: var(--ui-color-muted);
+  font-size: 0.48rem;
+  font-weight: 800;
   line-height: 1;
+}
+
+.theme-toggle__switch {
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 0.1rem;
+  min-width: 0;
+  padding-left: 0.1rem;
+}
+
+.theme-toggle__cell {
+  display: grid;
+  grid-template-columns: auto auto;
+  gap: 0.2rem;
+  align-items: center;
+  justify-content: center;
+  min-height: 1.68rem;
+  border: 1px solid transparent;
+  color: var(--ui-color-muted);
+  line-height: 1;
+  padding: 0 0.22rem;
   white-space: nowrap;
 }
 
+.theme-toggle__cell[data-active="true"] {
+  border-color: var(--ui-color-accent);
+  background: var(--ui-color-accent);
+  color: var(--ui-color-accent-contrast);
+}
+
+.theme-toggle__cell > span {
+  color: currentColor;
+}
+
+.theme-toggle:hover .theme-toggle__cell[data-active="false"] {
+  border-color: var(--ui-color-line);
+  color: var(--ui-color-text);
+}
+
+.theme-toggle .icon-glyph {
+  width: 0.82rem;
+  height: 0.82rem;
+  border: 0;
+  background: transparent;
+  color: currentColor;
+}
+
+.theme-toggle .icon-glyph svg {
+  width: 0.78rem;
+  height: 0.78rem;
+}
+
 .icon-glyph {
   display: inline-grid;
   width: 1.55rem;