feat(night-light): optional auto-on schedule (time window)

Night Light was all-or-nothing. Add an optional schedule with From/To time
inputs so the warm overlay only shows during set hours and toggles itself on/off
automatically (the overlay re-checks every minute; no reload). Overnight windows
that wrap midnight (e.g. 21:00 -> 07:00) are handled.

Window logic is the pure, unit-tested isWithinTimeWindow/parseHHMM in
utils/timeWindow.ts. New settings: nightLightSchedule/Start/End (default
21:00-07:00).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/settings/general/General.tsx

@@ -96,6 +96,7 @@ import {
   useThemes,
 } from '../../../hooks/useTheme';
 import { stopPropagation } from '../../../utils/keyboard';
+import { pickerInputStyle } from '../../../utils/datetimeInput';
 import { BG_OPTIONS, getChatBg } from '../../lotus/chatBackground';
 import { resetBootSequence, runLotusBootSequence } from '../../../../lotus-boot';
 import { useMessageLayoutItems } from '../../../hooks/useMessageLayout';
@@ -435,6 +436,12 @@ function Appearance() {
   const [lotusTerminal, setLotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
   const [nightLightEnabled, setNightLightEnabled] = useSetting(settingsAtom, 'nightLightEnabled');
   const [nightLightOpacity, setNightLightOpacity] = useSetting(settingsAtom, 'nightLightOpacity');
+  const [nightLightSchedule, setNightLightSchedule] = useSetting(
+    settingsAtom,
+    'nightLightSchedule',
+  );
+  const [nightLightStart, setNightLightStart] = useSetting(settingsAtom, 'nightLightStart');
+  const [nightLightEnd, setNightLightEnd] = useSetting(settingsAtom, 'nightLightEnd');
   const [glassmorphismSidebar, setGlassmorphismSidebar] = useSetting(
     settingsAtom,
     'glassmorphismSidebar',
@@ -567,23 +574,66 @@ function Appearance() {
         {nightLightEnabled && (
           <Box
             direction="Column"
-            gap="100"
+            gap="300"
             style={{ padding: `0 ${config.space.S400} ${config.space.S300}` }}
           >
-            <Text size="T200" priority="300">
-              Intensity: {nightLightOpacity}%
-            </Text>
-            <input
-              aria-label="Night light intensity"
-              type="range"
-              min={5}
-              max={80}
-              value={nightLightOpacity}
-              onChange={(e: React.ChangeEvent<HTMLInputElement>) =>
-                setNightLightOpacity(parseInt(e.target.value, 10))
-              }
-              style={{ width: '100%', accentColor: color.Primary.Main }}
-            />
+            <Box direction="Column" gap="100">
+              <Text size="T200" priority="300">
+                Intensity: {nightLightOpacity}%
+              </Text>
+              <input
+                aria-label="Night light intensity"
+                type="range"
+                min={5}
+                max={80}
+                value={nightLightOpacity}
+                onChange={(e: React.ChangeEvent<HTMLInputElement>) =>
+                  setNightLightOpacity(parseInt(e.target.value, 10))
+                }
+                style={{ width: '100%', accentColor: color.Primary.Main }}
+              />
+            </Box>
+            <Box alignItems="Center" justifyContent="SpaceBetween" gap="200">
+              <Box direction="Column">
+                <Text size="T300">Schedule</Text>
+                <Text size="T200" priority="300">
+                  Only tint during the hours below
+                </Text>
+              </Box>
+              <Switch
+                variant="Primary"
+                value={nightLightSchedule}
+                onChange={setNightLightSchedule}
+              />
+            </Box>
+            {nightLightSchedule && (
+              <Box gap="200">
+                <Box direction="Column" gap="100" style={{ flex: 1 }}>
+                  <Text as="label" htmlFor="night-light-start" size="T200" priority="400">
+                    From
+                  </Text>
+                  <input
+                    id="night-light-start"
+                    type="time"
+                    value={nightLightStart}
+                    onChange={(e) => setNightLightStart(e.target.value)}
+                    style={pickerInputStyle(color, config)}
+                  />
+                </Box>
+                <Box direction="Column" gap="100" style={{ flex: 1 }}>
+                  <Text as="label" htmlFor="night-light-end" size="T200" priority="400">
+                    To
+                  </Text>
+                  <input
+                    id="night-light-end"
+                    type="time"
+                    value={nightLightEnd}
+                    onChange={(e) => setNightLightEnd(e.target.value)}
+                    style={pickerInputStyle(color, config)}
+                  />
+                </Box>
+              </Box>
+            )}
           </Box>
         )}
       </SequenceCard>