feat: 添加好友功能并集成 LiteLLM 代理服务

- 新增好友搜索、添加、好友列表功能
- 集成 LiteLLM 代理服务及多模型定价配置
- 更新 iOS CocoaPods 配置
- 更新 .gitignore 和环境变量配置

backend/tests/unit/core/agent/test_init_data.py

@@ -31,3 +31,26 @@ def test_seed_data_does_not_keep_legacy_deepseek_alias() -> None:
     catalog = load_llm_catalog()
 
     assert all(entry["model_code"] != "deepseek-v3.2" for entry in catalog["llms"])
+
+
+def test_llm_catalog_contains_litellm_routing_and_pricing_fields() -> None:
+    catalog = load_llm_catalog()
+
+    for entry in catalog["llms"]:
+        assert set(entry.keys()) == {
+            "model_code",
+            "factory_name",
+            "litellm_model",
+            "pricing_tiers",
+        }
+        assert isinstance(entry["litellm_model"], str)
+        assert "/" in entry["litellm_model"]
+        pricing_tiers = entry["pricing_tiers"]
+        assert isinstance(pricing_tiers, list)
+        assert len(pricing_tiers) > 0
+        for tier in pricing_tiers:
+            assert isinstance(tier, dict)
+            assert int(tier["max_prompt_tokens"]) > 0
+            assert float(tier["input_cost_per_token"]) >= 0
+            assert float(tier["output_cost_per_token"]) >= 0
+            assert float(tier["cache_hit_cost_per_token"]) >= 0