feat: add per-user trial control in admin panel (backend + UI)

src/app/admin/students/[studentId]/page.tsx

@@ -1,4 +1,4 @@
-"use client"
+"use client"
 
 import { fetchWithAuth } from "@/lib/apiClient";
 import { useEffect, useState } from "react"
@@ -45,6 +45,8 @@ export default function StudentKundliPage() {
   const [editTier, setEditTier] = useState("")
   const [editStreak, setEditStreak] = useState(0)
   const [editExam, setEditExam] = useState("")
+  const [trialDays, setTrialDays] = useState(15)
+  const [grantingTrial, setGrantingTrial] = useState(false)
 
   useEffect(() => {
     fetchWithAuth(`/api/admin/students/${studentId}`)
@@ -370,6 +372,66 @@ export default function StudentKundliPage() {
           </CardContent>
         </Card>
       )}
+      {/* Trial Control Card */}
+      <Card className="border-amber-500/30 bg-amber-500/5 shadow-sm">
+        <CardHeader>
+          <CardTitle className="flex items-center gap-2 text-base text-amber-500">
+            <Flame size={16} className="text-amber-500" /> Trial Access Control
+          </CardTitle>
+        </CardHeader>
+        <CardContent className="space-y-4">
+          <div className="flex flex-wrap items-end gap-4">
+            <div className="space-y-1.5">
+              <label className="text-xs font-bold text-muted-foreground uppercase tracking-wider">Current Trial End</label>
+              <p className="text-sm font-semibold">
+                {data.trial_end ? (
+                  <span className={new Date(data.trial_end) > new Date() ? "text-green-500" : "text-red-500"}>
+                    {formatDate(data.trial_end)} ({new Date(data.trial_end) > new Date() ? "Active" : "Expired"})
+                  </span>
+                ) : (
+                  <span className="text-muted-foreground">No trial set</span>
+                )}
+              </p>
+            </div>
+            <div className="space-y-1.5">
+              <label className="text-xs font-bold text-muted-foreground uppercase tracking-wider">Grant Trial (days)</label>
+              <div className="flex gap-2">
+                <input
+                  type="number"
+                  min={0}
+                  max={365}
+                  value={trialDays}
+                  onChange={e => setTrialDays(Number(e.target.value))}
+                  className="w-24 bg-background border border-border rounded-lg px-3 py-2 text-sm font-bold focus:outline-none focus:ring-2 focus:ring-amber-500"
+                />
+                <Button
+                  onClick={async () => {
+                    setGrantingTrial(true)
+                    try {
+                      const res = await fetchWithAuth(`/api/admin/students/${studentId}`, {
+                        method: "PATCH",
+                        headers: { "Content-Type": "application/json" },
+                        body: JSON.stringify({ trial_days: trialDays }),
+                      })
+                      if (!res.ok) throw new Error("Failed")
+                      const fresh = await fetchWithAuth(`/api/admin/students/${studentId}`).then(r => r.json())
+                      setData(fresh)
+                      alert(`Trial ${trialDays > 0 ? `granted for ${trialDays} days` : 'removed'} successfully!`)
+                    } catch { alert("Failed to update trial") }
+                    finally { setGrantingTrial(false) }
+                  }}
+                  disabled={grantingTrial}
+                  className="bg-amber-500 text-black hover:bg-amber-400 font-bold gap-2"
+                >
+                  {grantingTrial ? <RefreshCw size={14} className="animate-spin" /> : <CheckCircle2 size={14} />}
+                  {trialDays > 0 ? `Grant ${trialDays}d Trial` : "Remove Trial"}
+                </Button>
+              </div>
+              <p className="text-xs text-muted-foreground">Set 0 to remove trial. Trial starts from now.</p>
+            </div>
+          </div>
+        </CardContent>
+      </Card>
     </div>
   )
 }