Add GitHub Copilot CLI installer provider

[SrFlipFlop]

Why

GitHub Copilot CLI was also verified as a working Burp MCP client, but setting it up currently requires users to manually create or edit ~/.copilot/mcp-config.json and wire in the packaged proxy jar with the correct --sse-url arguments.

That makes Copilot CLI setup more error-prone than the built-in Claude Desktop installer path. Adding a dedicated installer button makes the working Burp configuration reproducible and removes the need for users to hand-edit the MCP config for the common setup.

What changed

• add a new GitHubCopilotCliProvider installer
• register an Install to GitHub Copilot CLI button in the MCP installation panel
• extract or reuse the packaged mcp-proxy-all.jar via ProxyJarManager
• create or update ~/.copilot/mcp-config.json
• add or replace the mcpServers.burp entry with the tested local stdio proxy configuration
• preserve unrelated Copilot CLI MCP config entries when updating the file
• add tests covering config creation and replacement behavior

Scope

This PR only adds automatic installation for GitHub Copilot CLI.

It does not:

• add installers for other clients
• change the MCP server runtime behavior
• modify the existing Claude Desktop installer flow

Related issues

• Builds on the client setup work documented in #83.
• Completes another verified manual client installation path from the README examples.
• Helps with #46 by making one tested client easier to configure.
• Related to #38, which asks for clearer setup outside the Claude Desktop happy path.
• May help users hitting #42 by reducing manual config mistakes around proxy and endpoint setup.

Manual verification

• verified that GitHub Copilot CLI works against a local Burp MCP server through mcp-proxy-all.jar
• verified installer output writes a valid mcp-config.json entry for mcpServers.burp
• verified existing Copilot CLI MCP config entries are preserved while the Burp entry is updated

Tests

• added focused tests for Copilot CLI config creation
• added focused tests for Copilot CLI config merge/replacement behavior
• ran ./gradlew test