Let leaving admins choose who takes over the group (task #46)

Original ask: when the only admin leaves a group, let them pick a
specific successor instead of always auto-promoting the longest-tenured
member. Keep "auto" available, with bilingual labels.

Changes:
- lib/api-spec/openapi.yaml: extend POST /conversations/{id}/leave with
  an optional JSON body { successorId?: number | null }.
- Regenerated lib/api-client-react and lib/api-zod via api-spec codegen.
- artifacts/api-server/src/routes/conversations.ts: parse the new body,
  and when the leaver is the only admin, promote the requested successor
  if one is provided and is a current member; otherwise fall back to the
  existing oldest-member auto-promotion. Returns 400 if successorId is
  not a remaining member.
- artifacts/teaboy-os/src/pages/chat.tsx:
  - Track a successorChoice state ("auto" | userId).
  - In the leave confirmation dialog, when the user is the sole admin
    and there are other members, render a radio-list chooser with an
    "Auto" option (default) plus each remaining member.
  - Pass { successorId } to the leave mutation when a specific member
    is chosen; pass {} for auto.
  - Reset choice on success.
- artifacts/teaboy-os/src/locales/{en,ar}.json: added successorTitle,
  successorHelp, successorAuto strings.

Verification:
- pnpm -w run typecheck passes for libs and all artifacts.
- Attempted an end-to-end browser test; the run was interrupted before
  completion. Backend logic and UI wiring were validated by reading
  through the code paths and type system.

Replit-Task-Id: c9065bc1-ab4e-4a3b-a865-81754f5c2e5a

lib/api-client-react/src/generated/api.schemas.ts

@@ -562,6 +562,14 @@ export interface AdminAppOpensByUser {
   opens: AppOpenByUserEntry[];
 }
 
+export type LeaveConversationBody = {
+  /** When the leaver is the only admin, optionally name a specific
+remaining member to promote. Omit (or send null) to keep the
+automatic behavior of promoting the longest-tenured member.
+ */
+  successorId?: number | null;
+};
+
 export type GetAdminStatsParams = {
   /**
    * Time range for trend stats. Use "custom" with from/to.

lib/api-client-react/src/generated/api.ts

@@ -37,6 +37,7 @@ import type {
   GetAdminStatsParams,
   HealthStatus,
   HomeStats,
+  LeaveConversationBody,
   LoginBody,
   MessageWithSender,
   Notification,
@@ -2988,11 +2989,14 @@ export const getLeaveConversationUrl = (id: number) => {
 
 export const leaveConversation = async (
   id: number,
+  leaveConversationBody?: LeaveConversationBody,
   options?: RequestInit,
 ): Promise<SuccessResponse> => {
   return customFetch<SuccessResponse>(getLeaveConversationUrl(id), {
     ...options,
     method: "POST",
+    headers: { "Content-Type": "application/json", ...options?.headers },
+    body: JSON.stringify(leaveConversationBody),
   });
 };
 
@@ -3003,14 +3007,14 @@ export const getLeaveConversationMutationOptions = <
   mutation?: UseMutationOptions<
     Awaited<ReturnType<typeof leaveConversation>>,
     TError,
-    { id: number },
+    { id: number; data: BodyType<LeaveConversationBody> },
     TContext
   >;
   request?: SecondParameter<typeof customFetch>;
 }): UseMutationOptions<
   Awaited<ReturnType<typeof leaveConversation>>,
   TError,
-  { id: number },
+  { id: number; data: BodyType<LeaveConversationBody> },
   TContext
 > => {
   const mutationKey = ["leaveConversation"];
@@ -3024,11 +3028,11 @@ export const getLeaveConversationMutationOptions = <
 
   const mutationFn: MutationFunction<
     Awaited<ReturnType<typeof leaveConversation>>,
-    { id: number }
+    { id: number; data: BodyType<LeaveConversationBody> }
   > = (props) => {
-    const { id } = props ?? {};
+    const { id, data } = props ?? {};
 
-    return leaveConversation(id, requestOptions);
+    return leaveConversation(id, data, requestOptions);
   };
 
   return { mutationFn, ...mutationOptions };
@@ -3037,7 +3041,7 @@ export const getLeaveConversationMutationOptions = <
 export type LeaveConversationMutationResult = NonNullable<
   Awaited<ReturnType<typeof leaveConversation>>
 >;
-
+export type LeaveConversationMutationBody = BodyType<LeaveConversationBody>;
 export type LeaveConversationMutationError = ErrorType<unknown>;
 
 /**
@@ -3050,14 +3054,14 @@ export const useLeaveConversation = <
   mutation?: UseMutationOptions<
     Awaited<ReturnType<typeof leaveConversation>>,
     TError,
-    { id: number },
+    { id: number; data: BodyType<LeaveConversationBody> },
     TContext
   >;
   request?: SecondParameter<typeof customFetch>;
 }): UseMutationResult<
   Awaited<ReturnType<typeof leaveConversation>>,
   TError,
-  { id: number },
+  { id: number; data: BodyType<LeaveConversationBody> },
   TContext
 > => {
   return useMutation(getLeaveConversationMutationOptions(options));

lib/api-spec/openapi.yaml

@@ -765,6 +765,20 @@ paths:
           required: true
           schema:
             type: integer
+      requestBody:
+        required: false
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                successorId:
+                  type: integer
+                  description: |
+                    When the leaver is the only admin, optionally name a specific
+                    remaining member to promote. Omit (or send null) to keep the
+                    automatic behavior of promoting the longest-tenured member.
+                  nullable: true
       responses:
         "200":
           description: Left conversation

lib/api-zod/src/generated/api.ts

@@ -946,6 +946,15 @@ export const LeaveConversationParams = zod.object({
   id: zod.coerce.number(),
 });
 
+export const LeaveConversationBody = zod.object({
+  successorId: zod
+    .number()
+    .nullish()
+    .describe(
+      "When the leaver is the only admin, optionally name a specific\nremaining member to promote. Omit (or send null) to keep the\nautomatic behavior of promoting the longest-tenured member.\n",
+    ),
+});
+
 export const LeaveConversationResponse = zod.object({
   success: zod.boolean(),
 });