feat: MSC4260 Report User, Bug #6 mutual exclusion, TDS toast compliance

- Add ReportUserModal.tsx — category dropdown + reason input, calls
  POST /_matrix/client/v3/users/{userId}/report via mx.http.authedRequest,
  inline success/error feedback, auto-closes 1500ms after success
- Wire Report User button into UserRoomProfile.tsx between UserModeration
  and UserDeviceSessions (hidden for own profile)
- Bug #6: enforce mutual exclusion between chat backgrounds and seasonal
  themes — ChatBgGrid clears seasonal→'off' on non-'none' pick;
  SeasonalBgGrid clears chatBackground→'none' on real theme pick;
  SeasonalEffect guards against legacy persisted state at render time
- TDS: strip all hardcoded hex/rgba fallbacks from LotusToastContainer.tsx
  (var(--lt-bg-card), --lt-accent-orange, --lt-text-primary/secondary,
  --lt-accent-orange-dim/border, --lt-box-glow-orange)
- Mark Bug #6 FIXED, MSC4260 DONE, toast TDS FIXED in LOTUS_BUGS.md and
  LOTUS_TODO.md; note EventReaders + CallControls already compliant

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -432,6 +432,7 @@ function Appearance() {
     settingsAtom,
     'seasonalThemeOverride',
   );
+  const [, setChatBackground] = useSetting(settingsAtom, 'chatBackground');
 
   return (
     <Box direction="Column" gap="100">
@@ -512,7 +513,10 @@ function Appearance() {
         <Box style={{ padding: `0 ${config.space.S400} ${config.space.S300}` }}>
           <SeasonalBgGrid
             value={seasonalThemeOverride ?? 'auto'}
-            onChange={(v) => setSeasonalThemeOverride(v)}
+            onChange={(v) => {
+              setSeasonalThemeOverride(v);
+              if (v !== 'auto' && v !== 'off') setChatBackground('none');
+            }}
           />
         </Box>
       </SequenceCard>
@@ -1671,6 +1675,7 @@ function SeasonalBgGrid({
 
 function ChatBgGrid() {
   const [chatBackground, setChatBackground] = useSetting(settingsAtom, 'chatBackground');
+  const [, setSeasonalThemeOverride] = useSetting(settingsAtom, 'seasonalThemeOverride');
   const [pauseAnimations] = useSetting(settingsAtom, 'pauseAnimations');
   const theme = useTheme();
   const isDark = theme.kind === ThemeKind.Dark;
@@ -1683,7 +1688,10 @@ function ChatBgGrid() {
             type="button"
             aria-label={opt.label}
             aria-pressed={chatBackground === opt.value}
-            onClick={() => setChatBackground(opt.value as ChatBackground)}
+            onClick={() => {
+              setChatBackground(opt.value as ChatBackground);
+              if (opt.value !== 'none') setSeasonalThemeOverride('off');
+            }}
             style={{
               display: 'block',
               width: toRem(76),