[Bug] Editing MCP server changes target port

Bug Description

I have a streamable-http MCP server running with a specific target port, which must match the port the MCP server is running with.

Then using the UI, I edited it to change an unrelated environment variable. But when it's restarted, the server now has a different (random) target port, which breaks the server.

Steps to Reproduce

1. Run a streamable-http MCP server like osv, either from the registry or as custom. Note the target port (8080 in osv's case).
2. Edit the server to change anything about it, like adding an env var.
3. Note the restarted server has a new, random target port.

Expected Behavior

The target port should remain unchanged.

Actual Behavior

The target port is reassigned to a random value.

Priority

Medium

Environment

• OS: macOS
• ToolHive UI version: 0.32.0

Additional Context

Before: target port (and related MCP_PORT and FASTMCP_PORT env vars) == 8931

After: target port and env vars changed to 56967

Start by reproducing the edit-and-restart flow in the ToolHive UI with a streamable-http MCP server, then trace how the edited server's target port is assigned during restart. Done means changing an unrelated setting preserves the existing target port and related MCP_PORT and FASTMCP_PORT values.