feat: VS Code / JetBrains extension

[itigges22]

Description

Wrap the atlas-proxy agent loop into IDE extensions so developers can use ATLAS directly from their editor without the terminal CLI.

Requirements

• VS Code extension that communicates with atlas-proxy's SSE streaming endpoint
• JetBrains plugin (IntelliJ, PyCharm, WebStorm, GoLand)
• Sidebar or panel showing pipeline progress (tool calls, V3 stages, scoring)
• Inline diff display for edit_file operations
• File creation/deletion reflected in IDE explorer
• Configuration via extension settings (proxy URL, model preferences)

Architecture

atlas-proxy already exposes an HTTP API with SSE streaming. The extension would be a thin client that:

1. Sends user prompts to POST /v1/chat/completions with stream: true
2. Renders SSE events as progress indicators
3. Applies file operations to the workspace

Context

This is a significant effort but would greatly improve the developer experience. The proxy does all the heavy lifting — the extension is primarily UI.