refactor(ui): unify Channels + Stats filter chips (R13 S2c step 4)

- channel-manager sync-status chips (F2) -> FilterChipGroup (rounded-lg -> the
  canonical rounded-full), controls-row alignment preserved via className
- channel-manager user-tag chips (multi-select) restyled to filterChipClass
  (rounded-lg -> rounded-full) so the whole manager chip set is one look
- stats system time-range chips (F4) -> FilterChipGroup (text-sm -> canonical)

Adds aria-label i18n (channels.filters.syncLabel, stats.rangeLabel; HU+EN).
Self-E2E'd: sync chips + tag chips rounded-full, view TABS stay rounded-lg
(their own canonical), stats 7/30/90d toggles. gate green (tsc/eslint-0/
vitest 136/knip/prettier). Branch not merged.

frontend/src/components/Stats.tsx

@@ -9,6 +9,7 @@ import { notify } from "../lib/notifications";
 import { LS, useAccountPersistedState } from "../lib/storage";
 import Tooltip from "./Tooltip";
 import { LoadingState, StateMessage } from "./QueryState";
+import FilterChipGroup from "./FilterChipGroup";
 import { Section, SettingRow } from "./ui/form";
 import { useMe } from "../lib/useMe";
 
@@ -228,18 +229,16 @@ function SystemStats() {
 
       <div className="flex items-center justify-between gap-3 mb-4">
         <h2 className="text-lg font-semibold">{t("stats.title")}</h2>
-        <div className="flex items-center gap-1">
-          {RANGES.map((d) => (
-            <button
-              key={d}
-              onClick={() => setDays(d)}
-              aria-pressed={days === d}
-              className="pill px-3 py-1.5 rounded-full text-sm border"
-            >
-              {t("stats.rangeDays", { count: d })}
-            </button>
-          ))}
-        </div>
+        <FilterChipGroup
+          ariaLabel={t("stats.rangeLabel")}
+          className="flex items-center gap-1.5"
+          options={RANGES.map((d) => ({
+            value: String(d),
+            label: t("stats.rangeDays", { count: d }),
+          }))}
+          value={String(days)}
+          onChange={(v) => setDays(Number(v))}
+        />
       </div>
 
       <p className="text-xs text-muted mb-4 leading-relaxed">