feat(server)!: require a logged-in account for every channel request

Drop unauthenticated guests from channels: the allow_guests setting, the
/guests endpoints and the guest seat table are gone, and requests without an
account session get 401 account_required. Share links are unaffected.
Contract version is now 8.0.0.

web/src/core-bridge/generated/api.ts

@@ -1,5 +1,5 @@
 // Generated from backend DTOs; do not edit.
-// backend-contract-sha256: 54ea3f00fa672e0241efbb9fc8e7ad9e8fc68415ec124e08f70657c2d57d9ff9
+// backend-contract-sha256: 655e918f3443073c270bdeb9ae4e69d79dacf83baa90dea1a0cdcfe71d2b8bd5
 
 export interface AccountChannelBody {
   channel_id: string;
@@ -88,7 +88,6 @@ export interface ChannelInfo {
 export type ChannelMode = 'enc' | 'raw';
 
 export interface ChannelSettings {
-  allow_guests: boolean;
   delete_policy: DeletePolicy;
   file_max_downloads: number;
   join_policy: JoinPolicy;
@@ -100,7 +99,6 @@ export interface ChannelSettings {
   ui_restrict_copy_download: boolean;
 }
 export interface ChannelSettingsPatch {
-  allow_guests?: boolean | null;
   delete_policy?: DeletePolicy | null;
   file_max_downloads?: number | null;
   join_password?: string | null;
@@ -171,10 +169,6 @@ export interface GoneLogBody {
   error: string;
   oldest_seq: number;
 }
-export interface GuestInfo {
-  endpoint_hash: string;
-  joined_at: number;
-}
 export interface InvitationBody {
   channel_id: string;
   created_at: number;