feat: add editing and MCP command handling, enhance SSE streaming with usage tracking

- Implemented `Edit` and `McpAdd` commands in the command parser and handler.
- Added a new `stream` module to the runtime for handling streaming events.
- Enhanced `SseParser` to parse usage information from SSE events.
- Introduced `ToolCallAccumulator` for tracking tool calls independently.
- Updated `AppStateRest` to include `app_config` and `MiscState` to track `effort_level` and `selected_index`.
- Modified `LlmClient` to support streaming responses with usage tracking.
- Improved error handling and retry logic in the streaming API calls.
- Added tests for new features and improved markdown rendering in the chat view.

src/app/runtime/stream/tools/mod.rs

@@ -1,10 +1,15 @@
 use super::turn::ParsedToolCall;
 use serde_json::{json, Value};
 
+/// Standalone tool-call delta accumulator, functionally equivalent to the accumulation
+/// logic built into `StreamedTurn::apply_event`. Reserved for callers that want to track
+/// tool-call deltas independently of a full `StreamedTurn` (e.g. a lighter-weight preview).
+#[allow(dead_code)]
 pub struct ToolCallAccumulator {
     calls: Vec<ParsedToolCall>,
 }
 
+#[allow(dead_code)]
 impl ToolCallAccumulator {
     pub fn new() -> Self {
         ToolCallAccumulator { calls: Vec::new() }