fix(ui): unify icon badges — solid tile + white glyph via shared helper

The labelled icon-badge tiles were inconsistent: some used a same-hue
light tile + colored glyph (e.g. the Settings 2FA row: success.light tile
+ success.main glyph — low contrast, the reported "badly visible" icon),
and the solid-tile ones used the bright .main fill in dark mode without
darkening, so a white glyph on bright green/amber was low-contrast too
(DashProfile's success badge was ~1.9:1).

Add a single `iconBadgeSx(color)` helper (theme.ts): solid `<color>.main`
fill + white glyph, darkened in dark mode (FILLED_DARK_BG) so white stays
legible; `default` = neutral grey. Applied to every badge so they can't
drift: StatCard, DashActivityFeed, DashProfile (2FA badge), Dashboard
(2FA banner icon), AttendanceHistory (month tile), and the Settings 2FA
row tile (now solid green when required / grey when optional + white lock,
instead of the low-contrast light-green tile). Also switched DashProfile's
backup-codes warning callout from warning.light to a subtle warning wash
so its amber text stays readable in dark mode.

tsc -b --noEmit, npm run build, vitest 152/152 all clean.

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

src/admin/pages/Dashboard.tsx

@@ -12,6 +12,7 @@ import { require2FAOptions } from "../lib/queries/settings";
 import { getCzechDate } from "../utils/dashboardHelpers";
 import { useApiMutation } from "../lib/queries/mutations";
 import { Card, Button, StatusChip, PageEnter } from "../ui";
+import { iconBadgeSx } from "../theme";
 import DashKpiCards from "../components/dashboard/DashKpiCards";
 import DashQuickActions from "../components/dashboard/DashQuickActions";
 import DashActivityFeed from "../components/dashboard/DashActivityFeed";
@@ -253,17 +254,18 @@ export default function Dashboard() {
           >
             <Box sx={{ display: "flex", alignItems: "center", gap: 1.5 }}>
               <Box
-                sx={{
-                  width: 40,
-                  height: 40,
-                  borderRadius: "50%",
-                  display: "flex",
-                  alignItems: "center",
-                  justifyContent: "center",
-                  bgcolor: "error.main",
-                  color: "#fff",
-                  flexShrink: 0,
-                }}
+                sx={[
+                  {
+                    width: 40,
+                    height: 40,
+                    borderRadius: "50%",
+                    display: "flex",
+                    alignItems: "center",
+                    justifyContent: "center",
+                    flexShrink: 0,
+                  },
+                  iconBadgeSx("error"),
+                ]}
               >
                 <svg
                   width="20"