azd tool: review Azure MCP Server install strategy (global npm vs npx)

## Problem

The Azure MCP Server install strategy uses global npm install (`npm install -g @azure/mcp`), but:

1. Most MCP server configurations use `npx` (no global install needed)
2. Installing globally doesn't configure the MCP server in any editor — user still needs manual wiring
3. Global install could conflict with local dev dependencies

## Questions to Resolve

- Is global npm install the recommended approach from the Azure MCP team?
- Should `azd tool install azure-mcp-server` also help with editor configuration?
- Should we surface "next steps" for MCP configuration after install?

## Context

Raised by @vhvb1989 in PR #7450 review. Current approach is by-design for initial release — global install is the simplest path. Revisit based on user feedback and Azure MCP team guidance.

## Related

- PR #7450
- Issue #7845 (Epic A: Core Command Group)