docs: Document MCP editor setup and migration safety

[Zfinix]

Summary

The serverpod mcp-server page documented the --server-dir flag and nothing else, so there was nowhere to send a reader who wants to connect an agent to their project. It also said nothing about force, which the migration tools accept and an agent can pass on its own.

This PR:

• Adds a "Set up your editor" section listing the six editors serverpod create configures and the config file each one gets.
• Adds a "Set up any other MCP client" section with the two commands Serverpod registers, so clients outside that list can be wired up by hand.
• Adds a "Migrations and your data" section warning that an agent decides on its own when to pass force, and to point the bridge at a development database.

The tool reference itself is generated and arrives separately through serverpod/serverpod#5711. Only the hand-maintained _mcp-server.md intro changes here, which the docs-sync generator preserves across runs.