fix: preserve DeepSeek medium reasoning effort

app/src/main/java/io/legado/app/domain/model/AiModels.kt

@@ -229,7 +229,6 @@ enum class AiReasoningLevel(val effort: String, val budgetTokens: Int) {
         val identity = "${provider.id} ${provider.name} ${provider.baseUrl}".lowercase()
         return when {
             "mimo" in identity || "xiaomi" in identity -> null
-            "deepseek" in identity && this == MEDIUM -> LOW.effort
             "deepseek" in identity ||
                 "openai" in identity ||
                 "anthropic" in identity ||

app/src/test/java/io/legado/app/domain/model/AiReasoningLevelTest.kt

@@ -0,0 +1,20 @@
+package io.legado.app.domain.model
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class AiReasoningLevelTest {
+
+    @Test
+    fun deepSeekUsesTheStandardMediumEffort() {
+        val provider = AiProviderConfig(
+            id = "deepseek",
+            name = "DeepSeek",
+            protocol = AiProtocol.OPENAI_CHAT_COMPLETIONS,
+            baseUrl = "https://api.deepseek.com",
+            apiKey = "test"
+        )
+
+        assertEquals("medium", AiReasoningLevel.MEDIUM.effortFor(provider))
+    }
+}