refactor: remove unused clearAllCredentials and log diagnostics helpers

clearAllCredentials() (secureCredentials.ts), clearLogs() and
dumpDownloadDiagnostics() (log.tsx) have no callers anywhere in the tree.
Carried over from the original #1347 cleanup.

utils/log.tsx

@@ -72,21 +72,6 @@ export const readFromLog = (): LogEntry[] => {
   return logs ? JSON.parse(logs) : [];
 };
 
-export const clearLogs = () => {
-  storage.remove("logs");
-};
-
-export const dumpDownloadDiagnostics = (extra: any = {}) => {
-  const diagnostics = {
-    timestamp: new Date().toISOString(),
-    processes: extra?.processes || [],
-    nativeTasks: extra?.nativeTasks || [],
-    focusedProcess: extra?.focusedProcess || null,
-  };
-  writeDebugLog("Download diagnostics", diagnostics);
-  return diagnostics;
-};
-
 export function useLog() {
   const context = useContext(LogContext);
   if (context === null) {

utils/secureCredentials.ts

@@ -203,27 +203,6 @@ export async function hasAccountCredential(
   return stored !== null;
 }
 
-/**
- * Delete all credentials for all accounts on all servers.
- */
-export async function clearAllCredentials(): Promise<void> {
-  const previousServers = getPreviousServers();
-
-  for (const server of previousServers) {
-    for (const account of server.accounts) {
-      const key = credentialKey(server.address, account.userId);
-      await SecureStore.deleteItemAsync(key);
-    }
-  }
-
-  // Clear all accounts from servers
-  const clearedServers = previousServers.map((server) => ({
-    ...server,
-    accounts: [],
-  }));
-  storage.set("previousServers", JSON.stringify(clearedServers));
-}
-
 /**
  * Add or update an account in a server's accounts list.
  */