🔗 Add URL Content Extraction Feature (#514)

* feat: add URL content extraction for AI diagram generation

* Changes made as recommended by Claude:

1. Added a request timeout to prevent server resources from being tied up (route.ts)
2. Implemented runtime validation for the API response shape (url-utils.ts)
3. Removed hardcoded English error messages and replaced them with localized strings (url-input-dialog.tsx)
4. Fixed the incorrect i18n namespace (changed from pdf.* to url.*) (url-input-dialog.tsx and en/ja/zh.json)

* chore: restore package.json and package-lock.json

* fix: use i18n strings for URL dialog error messages

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

components/url-input-dialog.tsx

@@ -0,0 +1,116 @@
+"use client"
+
+import { Link, Loader2 } from "lucide-react"
+import { useState } from "react"
+import { Button } from "@/components/ui/button"
+import {
+    Dialog,
+    DialogContent,
+    DialogDescription,
+    DialogFooter,
+    DialogHeader,
+    DialogTitle,
+} from "@/components/ui/dialog"
+import { Input } from "@/components/ui/input"
+import { useDictionary } from "@/hooks/use-dictionary"
+
+interface UrlInputDialogProps {
+    open: boolean
+    onOpenChange: (open: boolean) => void
+    onSubmit: (url: string) => void
+    isExtracting: boolean
+}
+
+export function UrlInputDialog({
+    open,
+    onOpenChange,
+    onSubmit,
+    isExtracting,
+}: UrlInputDialogProps) {
+    const dict = useDictionary()
+    const [url, setUrl] = useState("")
+    const [error, setError] = useState("")
+
+    const handleSubmit = () => {
+        setError("")
+
+        if (!url.trim()) {
+            setError(dict.url.enterUrl)
+            return
+        }
+
+        try {
+            new URL(url)
+        } catch {
+            setError(dict.url.invalidFormat)
+            return
+        }
+
+        onSubmit(url.trim())
+    }
+
+    const handleKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
+        if (e.key === "Enter" && !isExtracting) {
+            e.preventDefault()
+            handleSubmit()
+        }
+    }
+
+    return (
+        <Dialog open={open} onOpenChange={onOpenChange}>
+            <DialogContent className="sm:max-w-md">
+                <DialogHeader>
+                    <DialogTitle>{dict.url.title}</DialogTitle>
+                    <DialogDescription>
+                        {dict.url.description}
+                    </DialogDescription>
+                </DialogHeader>
+
+                <div className="space-y-4">
+                    <div className="space-y-2">
+                        <Input
+                            value={url}
+                            onChange={(e) => {
+                                setUrl(e.target.value)
+                                setError("")
+                            }}
+                            onKeyDown={handleKeyDown}
+                            placeholder="https://example.com/article"
+                            disabled={isExtracting}
+                            autoFocus
+                        />
+                        {error && (
+                            <p className="text-sm text-destructive">{error}</p>
+                        )}
+                    </div>
+                </div>
+
+                <DialogFooter>
+                    <Button
+                        variant="outline"
+                        onClick={() => onOpenChange(false)}
+                        disabled={isExtracting}
+                    >
+                        {dict.url.Cancel}
+                    </Button>
+                    <Button
+                        onClick={handleSubmit}
+                        disabled={isExtracting || !url.trim()}
+                    >
+                        {isExtracting ? (
+                            <>
+                                <Loader2 className="mr-2 h-4 w-4 animate-spin" />
+                                {dict.url.Extracting}
+                            </>
+                        ) : (
+                            <>
+                                <Link className="mr-2 h-4 w-4" />
+                                {dict.url.extract}
+                            </>
+                        )}
+                    </Button>
+                </DialogFooter>
+            </DialogContent>
+        </Dialog>
+    )
+}