feat(runtime): add streaming support to LlmDriver trait

- Add StreamChunk and StreamEvent types for Tauri event emission
- Add stream() method to LlmDriver trait with async-stream
- Implement Anthropic streaming with SSE parsing
- Implement OpenAI streaming with SSE parsing
- Add placeholder stream() for Gemini and Local drivers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/zclaw-runtime/src/driver/local.rs

@@ -1,10 +1,13 @@
 //! Local LLM driver (Ollama, LM Studio, vLLM, etc.)
 
 use async_trait::async_trait;
+use futures::{Stream, StreamExt};
 use reqwest::Client;
-use zclaw_types::Result;
+use std::pin::Pin;
+use zclaw_types::{Result, ZclawError};
 
 use super::{CompletionRequest, CompletionResponse, ContentBlock, LlmDriver, StopReason};
+use crate::stream::StreamChunk;
 
 /// Local LLM driver for Ollama, LM Studio, vLLM, etc.
 pub struct LocalDriver {
@@ -56,4 +59,14 @@ impl LlmDriver for LocalDriver {
             stop_reason: StopReason::EndTurn,
         })
     }
+
+    fn stream(
+        &self,
+        _request: CompletionRequest,
+    ) -> Pin<Box<dyn Stream<Item = Result<StreamChunk>> + Send + '_>> {
+        // Placeholder - return error stream
+        Box::pin(futures::stream::once(async {
+            Err(ZclawError::LlmError("Local driver streaming not yet implemented".to_string()))
+        }))
+    }
 }