feat(mui): soft-SaaS component defaults (pill buttons, 16px cards, pill chips)

Adds MuiButton, MuiCard, and MuiChip styleOverrides to the theme: pill-shaped
buttons (borderRadius 999) with a red-gradient containedPrimary, 16px soft-
shadow cards, and pill chips. Driven by a new failing test first (TDD).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/theme.test.ts

@@ -25,4 +25,11 @@ describe("MUI theme", () => {
   it("uses the base radius of 10", () => {
     expect(theme.shape.borderRadius).toBe(10);
   });
+
+  it("makes buttons pill-shaped and cards 16px by default", () => {
+    const btn = theme.components?.MuiButton?.styleOverrides?.root as any;
+    expect(btn?.borderRadius).toBe(999);
+    const card = theme.components?.MuiCard?.styleOverrides?.root as any;
+    expect(card?.borderRadius).toBe(16);
+  });
 });

src/admin/theme.ts

@@ -47,6 +47,30 @@ export const theme = createTheme({
     h6: { fontFamily: FONT_HEADING, fontWeight: 700 },
     button: { textTransform: "none", fontWeight: 600 },
   },
+  components: {
+    MuiButton: {
+      defaultProps: { disableElevation: true },
+      styleOverrides: {
+        root: { borderRadius: 999, paddingInline: "0.95rem" },
+        containedPrimary: {
+          backgroundImage: "linear-gradient(135deg, #e23a3a, #c01f1f)",
+          boxShadow: "0 5px 14px rgba(214,48,49,0.32)",
+        },
+      },
+    },
+    MuiCard: {
+      styleOverrides: {
+        root: {
+          borderRadius: 16,
+          boxShadow:
+            "0 6px 20px rgba(20,20,40,0.06), 0 1px 2px rgba(0,0,0,0.03)",
+        },
+      },
+    },
+    MuiChip: {
+      styleOverrides: { root: { borderRadius: 999, fontWeight: 700 } },
+    },
+  },
 });
 
 export const fonts = {