feat: T3-style agents window setup and distinct subagent labels

[hackernotfound]

Makes the VS Code agents window easy to set up like T3 and keeps subagents readable while they run.

Changes

• README gains "Make the agents window feel like T3": the settings to add, how to turn on VS Code's hidden Subagents pill, how to filter it to in-progress subagents, and how to open a subagent as a tab or a side pane.
• copilot-tools.md tells the model that VS Code labels subagents by description, and to make each one unique and numbered, such as Reviewer 1: security.
• Version 1.1.0.

Verified:

• node tools/check.mjs: 20/20.
• tools/eval.sh (Copilot CLI 1.0.91): 10/10. node tools/eval-vscode.mjs (VS Code 1.140 runtime): 10/10.
• Same-task prompt with three subagents: 1.0.0 repeated one description for all three in 1 of 3 runs. This build gave unique numbered descriptions in 3 of 3 runs.
• Every README step was checked in VS Code 1.140's agents window: chat tabs, credit usage on cards, External hidden, sandbox on with commands working, the Subagents pill listing and opening subagents, and cards opening side panes.