fix: refactor time range to single source of truth with correct dates

- Default range changed from 30d to 7d
- Presets (today/7d/30d) now directly set customStart/customEnd dates,
  eliminating duplicate getTimeRange() calculation
- "All" preset fetches actual data boundaries from /api/date-range
  and backfills the custom date picker
- Clicking "custom" opens popover without triggering data refresh;
  only confirm applies changes
- SQL trend dates cast to ::text to avoid pg driver Date timezone offset
- Fix created_at filter from < to <= for end timestamp

components/TimeRangeSelector.tsx

@@ -8,18 +8,14 @@ import { useTimeRange } from "@/lib/time-range-context";
 import { useI18n } from "@/lib/i18n";
 
 export function TimeRangeSelector() {
-  const { t, locale } = useI18n();
+  const { t } = useI18n();
   const { range, setRange, customStart, customEnd, setCustomStart, setCustomEnd } = useTimeRange();
   const [showPopover, setShowPopover] = useState(false);
-  const [localStart, setLocalStart] = useState(customStart);
-  const [localEnd, setLocalEnd] = useState(customEnd);
+  const [localStart, setLocalStart] = useState("");
+  const [localEnd, setLocalEnd] = useState("");
   const popoverRef = useRef<HTMLDivElement>(null);
   const containerRef = useRef<HTMLDivElement>(null);
 
-  // Sync local state when context changes
-  useEffect(() => { setLocalStart(customStart); }, [customStart]);
-  useEffect(() => { setLocalEnd(customEnd); }, [customEnd]);
-
   // Close popover on click outside
   useEffect(() => {
     if (!showPopover) return;
@@ -48,7 +44,9 @@ export function TimeRangeSelector() {
     if (range === "custom" && showPopover) {
       setShowPopover(false);
     } else {
-      setRange("custom");
+      // customStart/customEnd already reflects the current preset's dates
+      setLocalStart(customStart);
+      setLocalEnd(customEnd);
       setShowPopover(true);
     }
   }
@@ -56,6 +54,7 @@ export function TimeRangeSelector() {
   function handleConfirm() {
     setCustomStart(localStart);
     setCustomEnd(localEnd);
+    setRange("custom");
     setShowPopover(false);
   }
 
@@ -126,7 +125,6 @@ export function TimeRangeSelector() {
               </label>
               <input
                 type="date"
-                lang={locale === "zh" ? "zh-CN" : "en-US"}
                 value={localStart}
                 onChange={(e) => setLocalStart(e.target.value)}
                 className="input-glass w-full rounded-md px-3 py-1.5 text-xs font-[family-name:var(--font-geist-mono)]"
@@ -138,7 +136,6 @@ export function TimeRangeSelector() {
               </label>
               <input
                 type="date"
-                lang={locale === "zh" ? "zh-CN" : "en-US"}
                 value={localEnd}
                 onChange={(e) => setLocalEnd(e.target.value)}
                 className="input-glass w-full rounded-md px-3 py-1.5 text-xs font-[family-name:var(--font-geist-mono)]"