bugfix: Add missing type to array in MCP schema

[gitplaneta]

Summary
Copilot Agent Mode rejects the Metals MCP tool generate-scalafix-rule due to an invalid JSON Schema:

Failed to validate tool mcp_hello-world-m_generate-scalafix-rule: Error: tool parameters array type must have items.

The tool’s inputSchema.properties.targets is "type": "array" but lacks an "items" schema, causing Copilot’s validation to fail and agent mode to break.

Steps to Reproduce

1. sbt new scala/scala3.g8
2. code .
3. Start Metals MCP server and enable Copilot Agent Mode
4. Observe Copilot error

Evidence

• mcp.trace.json excerpt:

{
  "name": "generate-scalafix-rule",
  "description": "Generate a scalafix rule and run it on the current project.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "ruleImplementation": { "type": "string", "description": "The implementation of the scalafix rule to run, this should contain the actual scalafix rule implementation." },
      "description": { "type": "string", "description": "The description of the scalafix rule to run for later MCP invocations." },
      "targets": {
        "type": "array",
        "description": "The targets to run the rule on, if empty will run on the last focused target"
        // Missing "items": { ... }
      },
      "sampleCode": { "type": "string", "description": "Sample code that we are trying to match in the rule, if nothing was matched an error will be returned with the structure of this sample." },
      "fileToRunOn": { "type": "string", "description": "File to run it all, if empty will run on all files in given targets" }
    },
    "required": ["description", "ruleImplementation"]
  }
}

[tgodzik]

LGTM! Thanks!