Improve Sourcegraph tool with context window and fix diagnostics

- Add context_window parameter to control code context display
- Fix LSP diagnostics notification handling with proper async waiting
- Switch to keyword search pattern for better results
- Add Sourcegraph tool to task agent

🤖 Generated with termai
Co-Authored-By: termai <noreply@termai.io>

internal/llm/agent/task.go

@@ -34,6 +34,7 @@ func NewTaskAgent(app *app.App) (Agent, error) {
 				tools.NewGlobTool(),
 				tools.NewGrepTool(),
 				tools.NewLsTool(),
+				tools.NewSourcegraphTool(),
 				tools.NewViewTool(app.LSPClients),
 			},
 			model:          model,