feat: AI 辅助修改行程（自然语言调整 + 单活动替代推荐）

- 新增 refinePlan / suggestAlternativeItems 到 ai.ts
- 新增 POST /api/blindbox/plan/refine（整体行程调整）
- 新增 POST /api/blindbox/plan/suggest-item（单活动 AI 替代 + POI 搜索）
- BlindboxPlan 底部新增自然语言输入框（方案 A）
- 编辑 modal 内新增 AI 推荐替代方案卡片（方案 B）
- export searchPois 供 suggest-item 路由复用

src/components/BlindboxPlan.tsx

@@ -38,6 +38,15 @@ import Button from "@/components/Button";
 import Modal from "@/components/Modal";
 import type { WeekendPlanData, PlanItem } from "@/types";
 
+interface AltSuggestion {
+  activity: string;
+  poi: string;
+  address: string;
+  lat: number;
+  lng: number;
+  reason: string;
+}
+
 interface BlindboxPlanProps {
   days: WeekendPlanData[];
   onAccept: () => void;
@@ -49,6 +58,7 @@ interface BlindboxPlanProps {
   onDaysChange?: (newDays: WeekendPlanData[]) => void;
   /** "lng,lat" 格式，用于 POI 搜索附近优先 */
   location?: string;
+  onRefine?: (instruction: string) => Promise<void>;
 }
 
 function guessCategory(activity: string): string | null {
@@ -265,6 +275,7 @@ export default function BlindboxPlan({
   regenerating,
   onDaysChange,
   location,
+  onRefine,
 }: BlindboxPlanProps) {
   const [dayIndex, setDayIndex] = useState(0);
   const scrollRef = useRef<HTMLDivElement>(null);
@@ -275,6 +286,10 @@ export default function BlindboxPlan({
 
   const [editingItem, setEditingItem] = useState<{ dayIndex: number; itemIndex: number } | null>(null);
   const [draft, setDraft] = useState<PlanItem | null>(null);
+  const [refineInput, setRefineInput] = useState("");
+  const [refining, setRefining] = useState(false);
+  const [suggestingAlt, setSuggestingAlt] = useState(false);
+  const [altSuggestions, setAltSuggestions] = useState<AltSuggestion[]>([]);
 
   useEffect(() => {
     scrollRef.current?.scrollTo({ top: 0, behavior: "smooth" });
@@ -314,6 +329,7 @@ export default function BlindboxPlan({
     onDaysChange(newDays);
     setEditingItem(null);
     setDraft(null);
+    setAltSuggestions([]);
   }
 
   // Cross-day move: immediately call onDaysChange
@@ -338,6 +354,34 @@ export default function BlindboxPlan({
     setDraft(null);
   }
 
+  async function handleRefine() {
+    if (!refineInput.trim() || refining || !onRefine) return;
+    setRefining(true);
+    try {
+      await onRefine(refineInput.trim());
+      setRefineInput("");
+    } finally {
+      setRefining(false);
+    }
+  }
+
+  async function handleSuggestAlt() {
+    if (!draft || suggestingAlt) return;
+    setSuggestingAlt(true);
+    try {
+      const res = await fetch("/api/blindbox/plan/suggest-item", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ activity: draft.activity, time: draft.time, location }),
+      });
+      if (!res.ok) return;
+      const data = await res.json();
+      setAltSuggestions(data.suggestions ?? []);
+    } finally {
+      setSuggestingAlt(false);
+    }
+  }
+
   if (!currentDay) return null;
 
   return (
@@ -446,6 +490,27 @@ export default function BlindboxPlan({
 
       {/* Fixed bottom bar — actions + day navigation */}
       <div className="shrink-0 border-t border-border/40 bg-background/80 pt-3 pb-[max(0.75rem,env(safe-area-inset-bottom))] backdrop-blur-lg">
+        {/* Refine input (Plan A) */}
+        {onRefine && (
+          <div className="mx-auto flex max-w-sm items-center gap-2 px-4 pb-2">
+            <input
+              value={refineInput}
+              onChange={(e) => setRefineInput(e.target.value)}
+              onKeyDown={(e) => { if (e.key === "Enter") handleRefine(); }}
+              placeholder="告诉 AI 你想怎么改..."
+              disabled={refining}
+              className="h-9 flex-1 rounded-xl bg-surface px-3 text-sm outline-none ring-1 ring-border focus:ring-purple-600 disabled:opacity-50"
+            />
+            <button
+              onClick={handleRefine}
+              disabled={!refineInput.trim() || refining}
+              className="flex h-9 w-9 items-center justify-center rounded-xl bg-purple-600/15 text-purple-400 disabled:opacity-30"
+            >
+              {refining ? <Loader2 size={15} className="animate-spin" /> : <Sparkles size={15} />}
+            </button>
+          </div>
+        )}
+
         {/* Day navigation */}
         {days.length > 1 && (
           <div className="mx-auto mb-2.5 flex max-w-sm items-center justify-center gap-2 px-4">
@@ -513,13 +578,13 @@ export default function BlindboxPlan({
       </div>
 
       {/* Edit item modal */}
-      <Modal open={!!editingItem && !!draft} onClose={() => { setEditingItem(null); setDraft(null); }} variant="sheet">
+      <Modal open={!!editingItem && !!draft} onClose={() => { setEditingItem(null); setDraft(null); setAltSuggestions([]); }} variant="sheet">
         {draft && editingItem && (
           <div className="flex flex-col gap-4">
             <div className="flex items-center justify-between">
               <h3 className="text-sm font-bold text-heading">编辑活动</h3>
               <button
-                onClick={() => { setEditingItem(null); setDraft(null); }}
+                onClick={() => { setEditingItem(null); setDraft(null); setAltSuggestions([]); }}
                 className="text-muted active:text-foreground"
               >
                 <X size={16} />
@@ -568,6 +633,38 @@ export default function BlindboxPlan({
                 onSelect={(s) => setDraft({ ...draft, poi: s.name, address: s.address, lat: s.lat, lng: s.lng })}
               />
 
+              {/* AI 推荐替代 (Plan B) */}
+              {altSuggestions.length === 0 ? (
+                <button
+                  onClick={handleSuggestAlt}
+                  disabled={suggestingAlt}
+                  className="flex items-center gap-1.5 self-start text-xs font-medium text-purple-400/70 active:text-purple-400 disabled:opacity-40"
+                >
+                  {suggestingAlt
+                    ? <><Loader2 size={12} className="animate-spin" /> 正在推荐...</>
+                    : <><Sparkles size={12} /> AI 推荐替代方案</>}
+                </button>
+              ) : (
+                <div className="flex flex-col gap-1.5">
+                  <span className="text-[11px] font-medium text-muted">选一个替代方案</span>
+                  {altSuggestions.map((alt, i) => (
+                    <button
+                      key={i}
+                      onClick={() => {
+                        setDraft({ ...draft, ...alt });
+                        setAltSuggestions([]);
+                      }}
+                      className="rounded-lg bg-elevated px-3 py-2 text-left ring-1 ring-border active:ring-purple-500"
+                    >
+                      <p className="text-xs font-bold text-heading">{alt.activity}</p>
+                      <p className="truncate text-[10px] text-muted">{alt.poi}</p>
+                      <p className="text-[10px] text-dim italic">{alt.reason}</p>
+                    </button>
+                  ))}
+                  <button onClick={() => setAltSuggestions([])} className="self-start text-[10px] text-dim">取消</button>
+                </div>
+              )}
+
               {days.length > 1 && (
                 <label className="flex flex-col gap-1">
                   <span className="text-[11px] font-medium text-muted">移动到其他天</span>