refactor(stage-4): partition monolithic main.py into modular APIRouters

app/routers/__init__.py

@@ -0,0 +1,40 @@
+from app.routers.auth import router as auth_router
+from app.routers.dictionary import router as dictionary_router
+from app.routers.listening import router as listening_router
+from app.routers.cards import router as cards_router
+from app.routers.srs import router as srs_router
+from app.routers.export import router as export_router
+from app.routers.reader import router as reader_router
+from app.routers.cefr import router as cefr_router
+from app.routers.grammar import router as grammar_router
+from app.routers.tasks import router as tasks_router
+from app.routers.lessons import router as lessons_router
+
+all_routers = [
+    auth_router,
+    dictionary_router,
+    listening_router,
+    cards_router,
+    srs_router,
+    export_router,
+    reader_router,
+    cefr_router,
+    grammar_router,
+    tasks_router,
+    lessons_router,
+]
+
+__all__ = [
+    "all_routers",
+    "auth_router",
+    "dictionary_router",
+    "listening_router",
+    "cards_router",
+    "srs_router",
+    "export_router",
+    "reader_router",
+    "cefr_router",
+    "grammar_router",
+    "tasks_router",
+    "lessons_router",
+]