refactor(stream-parsing): restructured stream utilities to use Web standard APIs and generic SSE parsing

- Refactored SSE stream parsing to use generic `readSseJson` utility instead of domain-specific handlers across multiple packages.
- Migrated from Node.js Buffer API to Web standard APIs (Uint8Array, TextDecoder, DataView) for cross-platform compatibility.
- Simplified stream transformation pipeline by consolidating multiple stream operations into unified `createTextLineSplitter` utility.
- Refactored `ptree.ts` to remove complex stream pumping infrastructure and simplify stderr handling with direct async iteration.
- Rewrote stream utilities to operate at binary level with byte-level parsing for improved efficiency and reduced string allocations.
- Updated TypeScript configuration to include DOM.AsyncIterable type definitions for async iterable DOM API support.

packages/coding-agent/src/cli/file-processor.ts

@@ -49,7 +49,7 @@ export async function processFileArguments(fileArgs: string[], options?: Process
 
 		if (mimeType) {
 			// Handle image file
-			const base64Content = buffer.toString("base64");
+			const base64Content = buffer.toBase64();
 			let attachment: ImageContent;
 			let dimensionNote: string | undefined;