Add integrated terminal panel with xterm.js and node-pty

[bobicloudvision]

Summary

This pull request introduces a built-in terminal panel to the editor layout. It uses xterm.js with fit and webgl addons for rendering and node-pty for an interactive shell. The terminal automatically initializes when a project is open, follows the project’s working directory, resizes responsively, and restarts when the project path changes.

Changes Made

Terminal integration

• Implemented EditorTerminal component rendering an embedded terminal panel with a sticky header.
• Added xterm.js with FitAddon and optional WebglAddon for high-quality rendering and auto-fit behavior.
• Wired node-pty via execNodePty to provide an interactive shell session.

Project-awareness and lifecycle

• Terminal visibility is gated by projectConfiguration.path and updates via onProjectConfigurationChangedObservable.
• Shell cwd is set relative to the current project path and re-initialized when the project changes.
• Clean disposal of addons, terminal, and PTY on unmount; safe restart logic on project changes.

Responsiveness and UX

• ResizeObserver triggers fit() for responsive sizing.
• Terminal resizes on layout changes and forwards size to PTY.
• Theming configured for editor look-and-feel with readable defaults and selection styling.

Benefits

• Improves productivity by enabling command execution without leaving the editor.
• Responsive and performant terminal rendering (WebGL fallback to canvas).
• Project-aware shell sessions reduce friction (correct cwd, auto-restart on project switch).
• Clean lifecycle management reduces leaks and ensures stability.