feat(privacy): delete all my messages in a room (#169)

Room Settings → General → Privacy: 'Your messages in this room' with a
Delete all… flow. The confirm dialog first counts your events with a
server-side sender-filtered /messages walk (live count), then asks to confirm
with the number — typing the room name above 50 — and offers 'Leave the room
afterwards'. Files are called out as not purged by a redaction.

The job runs outside React (closing settings is fine): sequential redactEvent
with 429 back-off, 404/already-redacted skipped, progress on the tile with
Cancel, pending ids persisted per room so a reload shows Resume/Discard, a
toast when done. State events are never touched; reactions, edits and thread
replies you sent are included; encrypted rooms work the same (nothing is
decrypted). Own events need no power level, so it is purely self-service.

Unit tests cover candidate filtering, the server filter, pagination, 429/404
handling and cancel. Verified headless: 62 of bob's events (60 messages, a
reaction, a thread reply) redacted in ~34 s while alice's 10 stayed; cancel at
17/40 → reload → Resume → 'Deleted 40 messages.'

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

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

@@ -15,6 +15,7 @@ import {
   RoomRetention,
   RoomShareInvite,
   RoomUpgrade,
+  DeleteMyMessages,
   RoomVoiceLimit,
 } from '../../common-settings/general';
 import { useRoomCreators } from '../../../hooks/useRoomCreators';
@@ -79,6 +80,10 @@ export function General({ requestClose }: GeneralProps) {
                 <Text size="L400">Advanced Options</Text>
                 <RoomUpgrade permissions={permissions} requestClose={requestClose} />
               </Box>
+              <Box direction="Column" gap="100">
+                <Text size="L400">Privacy</Text>
+                <DeleteMyMessages />
+              </Box>
             </Box>
           </PageContent>
         </Scroll>