fix: better mcp sanitization - #3842

Closes #3354
Closes #3245

You may read those for further background.

Repro

1. Use https://xmcp.dev to generate a dummy MCP server with a greet tool
2. Rename that greet tool to include a slash "/", e.g.

// ...
export const metadata: ToolMetadata = {
  name: "greet/tool",
  description: "Greet the user",
// ...

4. Add MCP server to opencode.json in the root of the repo.
5. Run opencode using Anthropic and ask something
   New MCP server in opencode.json 👇

"test-mcp-server": {
      "type": "remote",
      "url": "http://localhost:3001/mcp"
}

Changelog

Applied further sanitization to both tool names and client names.
Note, that I've seen a number of issues related to tool name length, I haven't looked into that yet.

Successful scenario A

Small footnote: debugging bun is such a PITA