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/components/dashboard/DashActivityFeed.tsx

@@ -2,6 +2,7 @@ import { Link as RouterLink } from "react-router-dom";
 import Box from "@mui/material/Box";
 import Typography from "@mui/material/Typography";
 import { Card, Button, EmptyState } from "../../ui";
+import { iconBadgeSx, type IconBadgeColor } from "../../theme";
 import {
   ENTITY_TYPE_LABELS,
   getActivityIconClass,
@@ -159,17 +160,20 @@ export default function DashActivityFeed({
                 }}
               >
                 <Box
-                  sx={{
-                    display: "flex",
-                    alignItems: "center",
-                    justifyContent: "center",
-                    width: 32,
-                    height: 32,
-                    borderRadius: "50%",
-                    flexShrink: 0,
-                    bgcolor: isDefault ? "grey.600" : `${badgeColor}.main`,
-                    color: "common.white",
-                  }}
+                  sx={[
+                    {
+                      display: "flex",
+                      alignItems: "center",
+                      justifyContent: "center",
+                      width: 32,
+                      height: 32,
+                      borderRadius: "50%",
+                      flexShrink: 0,
+                    },
+                    iconBadgeSx(
+                      isDefault ? "default" : (badgeColor as IconBadgeColor),
+                    ),
+                  ]}
                 >
                   {getActivityIcon(act.action)}
                 </Box>