feat: rename to pstack-copilot on the Agent Plugins 1.0 format

[hackernotfound]

Renames the plugin to pstack-copilot and moves it to the Agent Plugins 1.0 manifest format, so it passes awesome-copilot's spec check and has a name of its own in the marketplace. Released as 1.2.0.

Changes

Part	Before	After
Plugin name	pstack	pstack-copilot
plugin.json	legacy Copilot format with skills, hooks, displayName	Agent Plugins 1.0: $schema, schema properties only, extensions: {"com.github.copilot": {}}
Startup hook	hooks/, run via ${CLAUDE_PLUGIN_ROOT}	com.github.copilot/hooks/, run via ${PLUGIN_ROOT}
Install	copilot plugin install pstack@pstack-vscode	copilot plugin install pstack-copilot@pstack-vscode

• The folder stays plugins/pstack, so existing chat.pluginLocations paths keep working.
• The README adds an upgrade note for 1.1.1 installs.
• tools/check.mjs now fails if the manifest leaves the 1.0 schema or the hook command points at a missing script. The evals catch either name prefix.

Verified:

• node tools/check.mjs: 23/23
• awesome-copilot's external-plugin-quality-gates.mjs on f246e99: all pass, including spec compliance (it warned on v1.1.1) and the install smoke test
• copilot plugin install pstack-copilot@pstack-vscode from a local marketplace: v1.2.0, 54 skills
• Live evals: tools/eval.sh 10/10 on Copilot CLI 1.0.91, tools/eval-vscode.mjs 10/10 on VS Code 1.140.0's bundled runtime
• VS Code 1.140.0 agents window: Plugins lists pstack-copilot (54 skills, 1 hook), a new Copilot session quotes the hook's text, and the agent picker shows only Agent