fix(kernel): add map_err context to classroom LLM generation calls

Stage 1 (outline) and Stage 2 (scene) LLM calls now provide descriptive
error messages instead of propagating opaque driver errors.

Closes M11-02

crates/zclaw-kernel/src/generation/mod.rs

@@ -428,7 +428,10 @@ impl GenerationPipeline {
             plan_mode: false,
         };
 
-        let response = driver.complete(llm_request).await?;
+        let response = driver.complete(llm_request).await
+            .map_err(|e| zclaw_types::ZclawError::LlmError(
+                format!("Outline generation failed: {}", e)
+            ))?;
         let text = Self::extract_text_from_response_static(&response);
         self.parse_outline_from_text(&text, request)
     }
@@ -500,7 +503,10 @@ Use Chinese if the topic is in Chinese. Include vivid metaphors and analogies."#
             plan_mode: false,
         };
 
-        let response = driver.complete(llm_request).await?;
+        let response = driver.complete(llm_request).await
+            .map_err(|e| zclaw_types::ZclawError::LlmError(
+                format!("Scene '{}' generation failed: {}", item.title, e)
+            ))?;
         let text = Self::extract_text_from_response_static(&response);
         Self::parse_scene_from_text_static(&text, item, order)
     }