🔗 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>

lib/i18n/dictionaries/en.json

@@ -51,7 +51,8 @@
         "badResponse": "Bad response",
         "clickToEdit": "Click to edit",
         "editMessage": "Edit message",
-        "saveAndSubmit": "Save & Submit"
+        "saveAndSubmit": "Save & Submit",
+        "ExtractURL": "Extract from URL"
     },
     "examples": {
         "title": "Create diagrams with AI",
@@ -186,6 +187,15 @@
         "chars": "chars",
         "removeFile": "Remove file"
     },
+    "url": {
+        "title": "Extract Content from URL",
+        "description": "Paste a URL to extract and analyze its content",
+        "Extracting": "Extracting...",
+        "extract": "Extract",
+        "Cancel": "Cancel",
+        "enterUrl": "Please enter a URL",
+        "invalidFormat": "Invalid URL format"
+    },
     "reasoning": {
         "thinking": "Thinking...",
         "thoughtFor": "Thought for {duration} seconds",