fix(commands): /kick and /ban failures are no longer silent (#216)

rateLimitedActions now collects non-429 failures (and a 429 that exhausted its
retries) and returns them instead of swallowing them; existing callers ignore
the return. /kick and /ban turn the list into a CommandError whose message
names who and why, using the server's own sentence (MatrixError.data.error),
never the URL-bearing toString(); RoomInput's toast shows it verbatim.

Verified headless as a non-moderator: '/kick @alice' → "Could not kick
@alice:localhost: You cannot kick user @alice:localhost."; '/ban @nobody
@alice' → "Could not ban @nobody:localhost, @alice:localhost: You don't have
permission to ban".

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

src/app/utils/matrix.ts

@@ -467,15 +467,24 @@ export const declineInvite = async (mx: MatrixClient, roomId: string): Promise<v
   await mx.forget(roomId).catch(() => undefined);
 };
 
+export type RateLimitedFailure<T> = { item: T; error: MatrixError };
+
+/**
+ * Run `callback` over `data` sequentially, backing off on 429. Other errors do
+ * not stop the loop — they are collected and returned so callers can tell the
+ * user which items failed (a failed /kick used to vanish silently, #216).
+ */
 export const rateLimitedActions = async <T, R = void>(
   data: T[],
   callback: (item: T, index: number) => Promise<R>,
   maxRetryCount?: number,
-) => {
+): Promise<{ failures: RateLimitedFailure<T>[] }> => {
   let retryCount = 0;
 
   let actionInterval = 0;
 
+  const failures: RateLimitedFailure<T>[] = [];
+
   const sleepForMs = (ms: number) =>
     new Promise((resolve) => {
       setTimeout(resolve, ms);
@@ -486,6 +495,7 @@ export const rateLimitedActions = async <T, R = void>(
 
     if (err?.httpStatus === 429) {
       if (retryCount === maxRetryCount) {
+        failures.push({ item: dataItem, error: err });
         return;
       }
 
@@ -496,6 +506,8 @@ export const rateLimitedActions = async <T, R = void>(
       retryCount += 1;
 
       await performAction(dataItem, index);
+    } else if (err) {
+      failures.push({ item: dataItem, error: err });
     }
   };
 
@@ -509,6 +521,7 @@ export const rateLimitedActions = async <T, R = void>(
       await sleepForMs(actionInterval);
     }
   }
+  return { failures };
 };
 
 export const knockSupported = (version: string): boolean => {