feat: orphaned data cleanup, file deletion on message/account removal, and group DM improvements

- Add fileCleanup utility to delete uploaded files from disk on message/account deletion
- Add migration to clean orphaned DM channels, attachments, reactions, read states, and stale moderator refs
- Add FK constraints on dm_message_id in attachments and dm_reactions schema
- Make bans.bannedBy and voiceRestrictions.moderatorId nullable for deleted moderators
- Transfer group DM ownership on member leave or account deletion
- Fully clean up orphaned DM channels (zero members) including files
- Add "Leave Group" context menu for group DMs in ChannelSidebar
- Add leaveDm action to spaceStore

packages/web/src/stores/spaceStore.ts

@@ -46,6 +46,7 @@ interface SpaceState {
   addDmMember: (dmChannelId: string, user: User) => void;
   removeDmMember: (dmChannelId: string, userId: string) => void;
   closeDm: (id: string) => Promise<void>;
+  leaveDm: (id: string) => Promise<void>;
   loadSpaces: () => Promise<void>;
   loadSpaceDetail: (spaceId: string) => Promise<void>;
   loadDmChannels: () => Promise<void>;
@@ -130,6 +131,15 @@ export const useSpaceStore = create<SpaceState>((set, get) => ({
     }));
   },
 
+  leaveDm: async (id) => {
+    const origin = get().channelOriginMap.get(id) || '';
+    const targetApi = getApiForOrigin(origin);
+    await targetApi.dm.leave(id);
+    set((state) => ({
+      dmChannels: state.dmChannels.filter(c => c.id !== id)
+    }));
+  },
+
   loadSpaces: async () => {
     try {
       const spaces =await api.spaces.list();