fix(filesystem): fix move_file outputSchema to return array of content objects

[Jim1874]

Summary

move_file outputSchema was incorrectly returning a raw string instead of
an array of content objects [{type:'text', text:'...'}].

This caused MCP protocol -32602 validation errors in automated callers.

Closes #3093

[Jim1874]

Note: Test failure is a pre-existing issue in main

The Test filesystem failure for structuredContent in move_file is not caused by this PR. I verified:

1. Ran the same test against origin/main — it also fails with the same error: expected undefined to be defined
2. The structuredContent field is not being returned by move_file in the MCP SDK client response — this is a pre-existing bug in the codebase, not introduced by this PR

This PR only fixes the outputSchema declaration from { content: z.string() } to { content: z.array(...) } to match the actual content return value. The structuredContent test issue should be addressed separately.

Files changed: src/filesystem/index.ts — only the outputSchema field was modified.