fix: comprehensive P0 quality pass — audit findings resolved

- ReportRoomModal: use mx.reportRoom() SDK method, fix undefined CSS vars
  (--mx-surface/border → folds color tokens), add role/aria-modal/aria-labelledby,
  accessible select/input labels, per-error-code messages, auto-close on success
- About.tsx: clickable matrix_id + email_address links (Text as="a"), AbortController
  cleanup, runtime JSON type guard, loading state, role display for all role values,
  remove classList theming hack, use mx.getHomeserverUrl()
- RoomViewHeader: useLocalRoomName for header title, useReportRoomSupported gate,
  hide Invite/Settings/Report for server notice rooms, isCreator guard on Report,
  FocusTrap returnFocusOnDeactivate on topic overlay, Server Notice chip tooltip
- RoomInput: replace raw <div> with folds <Box> for server notice read-only message
- EditHistoryModal: isRawEditEvent type guard, handle next_batch truncation,
  getVersionBody handles formatted_body (strips HTML for text display),
  role/aria-modal/aria-labelledby accessibility, guard for undefined eventId,
  use config.space tokens (remove var(--mx-spacing-*) strings)
- RoomNavItem: remove duplicate getExistingContent (use exported getLocalRoomNamesContent),
  maxLength={255} on rename input, fix FocusTrap nesting (renameDialog state moved to
  RoomNavItem_, RenameRoomDialog rendered outside menu, menu closes before dialog opens),
  pencil icon opacity via config.opacity.P300
- useRoomMeta: export getLocalRoomNamesContent for reuse
- RoomIntro: useLocalRoomName, formatted topic viewer with Overlay/FocusTrap/RoomTopicViewer
- CallRoomName: useLocalRoomName for consistent rename display in call overlay
- General.tsx: fix #980000/#FF6B00 hardcoded hex → color tokens/CSS vars, URL Preview
  capitalization, improved encrypted preview warning text + Warning chip, add
  description to plain urlPreview setting
- sanitize.ts: fix hex color regex to support 3/4/6/8 digit hex (CSS4 #RGBA, #RRGGBBAA)

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

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

@@ -14,6 +14,7 @@ import {
   Box,
   Button,
   Chip,
+  color,
   config,
   Header,
   Icon,
@@ -408,8 +409,8 @@ function Appearance() {
                   title="Replay boot sequence"
                   style={{
                     background: 'transparent',
-                    border: '1px solid rgba(255,107,0,0.35)',
-                    color: '#FF6B00',
+                    border: '1px solid var(--accent-orange-border)',
+                    color: 'var(--accent-orange)',
                     fontSize: '0.65rem',
                     padding: '0.2rem 0.6rem',
                     cursor: 'pointer',
@@ -964,14 +965,14 @@ function ChatBgGrid() {
               cursor: 'pointer',
               border:
                 chatBackground === opt.value
-                  ? '2px solid #980000'
+                  ? `2px solid ${color.Critical.Main}`
                   : '2px solid rgba(128,128,128,0.25)',
               padding: 0,
               overflow: 'hidden',
               ...getChatBg(opt.value as ChatBackground, isDark),
             }}
           />
-          <Text size="T200" style={chatBackground === opt.value ? { color: '#980000' } : undefined}>
+          <Text size="T200" style={chatBackground === opt.value ? { color: color.Critical.Main } : undefined}>
             {opt.label}
           </Text>
         </Box>
@@ -1195,14 +1196,32 @@ function Messages() {
       </SequenceCard>
       <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
         <SettingTile
-          title="Url Preview"
+          title="URL Preview"
+          description="Your homeserver fetches and caches link previews. It will see the URLs of all links you preview."
           after={<Switch variant="Primary" value={urlPreview} onChange={setUrlPreview} />}
         />
       </SequenceCard>
       <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
         <SettingTile
-          title="Url Preview in Encrypted Room"
-          description="URL previews in encrypted rooms are fetched by your homeserver, which sees the URL but not the message content."
+          title="URL Preview in Encrypted Rooms"
+          description={
+            <Box direction="Column" gap="100">
+              <Text size="T200" priority="300">
+                Your homeserver fetches link previews on your behalf. It cannot decrypt your
+                messages, but will see every URL you preview in encrypted rooms, potentially
+                revealing conversation topics.
+              </Text>
+              <Chip
+                variant="Warning"
+                fill="Soft"
+                radii="300"
+                size="400"
+                style={{ alignSelf: 'flex-start' }}
+              >
+                <Text size="T200">Privacy risk — enabled by default</Text>
+              </Chip>
+            </Box>
+          }
           after={<Switch variant="Primary" value={encUrlPreview} onChange={setEncUrlPreview} />}
         />
       </SequenceCard>