Add word-book practice, iOS app shell, and fix embedded WebView blank screen.

Ship dual-track learning (daily accumulation vs textbook),沪教/商务词书 APIs and UI, native iOS wrapper with bundled H5, and production book import on deploy.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/services/translation_service.py

@@ -34,7 +34,7 @@ class TranslationService:
                 entry.example_en,
                 entry.example_cn,
             )
-        return self._placeholder(text, text, "en", "zh")
+        return self._placeholder(text, "en", "zh")
 
     def _zh_to_en(self, db: Session, text: str) -> dict:
         entry = dictionary_service.lookup_zh(db, text)
@@ -48,7 +48,7 @@ class TranslationService:
                 entry.example_en,
                 entry.example_cn,
             )
-        return self._placeholder(text, f"[{text}]", "zh", "en")
+        return self._placeholder(text, "zh", "en")
 
     def _build_response(
         self,
@@ -68,17 +68,19 @@ class TranslationService:
             "phonetic": phonetic,
             "example_en": example_en,
             "example_cn": example_cn,
+            "found": True,
         }
 
-    def _placeholder(self, source: str, target: str, source_lang: str, target_lang: str) -> dict:
+    def _placeholder(self, source: str, source_lang: str, target_lang: str) -> dict:
         return {
             "source_text": source,
-            "target_text": target,
+            "target_text": "",
             "source_lang": source_lang,
             "target_lang": target_lang,
             "phonetic": None,
-            "example_en": f"Example with {target}." if target_lang == "en" else None,
-            "example_cn": f"包含「{source}」的例句。" if source_lang == "zh" else None,
+            "example_en": None,
+            "example_cn": None,
+            "found": False,
         }