Clarify credentials username placeholder

Bug bounty alias accounts are nearly always emails, so a bare
"username" placeholder read like a handle only. Say "email or
username" in both the creation dialog and the task detail tab.
The agent tool description already said "login name / email used".

web/src/app/(main)/function/tasks/detail/_tabs/credentials-tab.tsx

@@ -144,7 +144,7 @@ export function CredentialsTab({ taskId }: { taskId: string }) {
         )}
         <div className="grid gap-2 sm:grid-cols-[1fr_1fr_1fr_auto]">
           <Input placeholder="domain (e.g. target.example.com)" value={domain} onChange={(e) => setDomain(e.target.value)} />
-          <Input placeholder="username" value={username} onChange={(e) => setUsername(e.target.value)} />
+          <Input placeholder="email or username" value={username} onChange={(e) => setUsername(e.target.value)} />
           <Input
             placeholder="password (empty = agent generates)"
             type="text"

web/src/app/(main)/function/tasks/page.tsx

@@ -3346,7 +3346,7 @@ function CreateTaskSheet({
                       onChange={(e) => setCredentials((prev) => prev.map((x, j) => (j === i ? { ...x, domain: e.target.value } : x)))}
                     />
                     <Input
-                      placeholder="username"
+                      placeholder="email or username"
                       value={c.username}
                       onChange={(e) => setCredentials((prev) => prev.map((x, j) => (j === i ? { ...x, username: e.target.value } : x)))}
                     />