Allow mcp configuration

[dacec354]

Problem

The GitHub MCP tools ( get_issue , create_pr , etc.) are listed as available tools, but calling them fails with Authentication Failed: Requires authentication .
There's no prompt, no setup flow, no hint in the UI telling the user why it failed or how to fix it.

A new user (like the one in #374) who's never used an AI coding agent before has no way to know they need to:

1. Create a GitHub Personal Access Token
2. Set GITHUB_PERSONAL_ACCESS_TOKEN in their environment
3. Restart Reasonix

The tools just quietly fail with a cryptic auth error.

Proposed change

allow changing env, command, args in config file and dashboard. builtin mcp can freeze command and args but at least expose env.

Scope check

• This belongs in core reasonix (not better as a separate npm package)
• I've read CLAUDE.md and CONTRIBUTING.md

[esengine]

Thanks — you've identified a real gap. State of things:

• Transport layer already accepts a per-server env overlay (StdioTransport in src/mcp/stdio.ts); it's just not plumbed through from the bridge call site in chat.tsx.
• The catalog already declares requiredEnv (github → GITHUB_PERSONAL_ACCESS_TOKEN), and reasonix mcp install prints it as "needs: …" — but there's no in-app way to actually set it after the fact.

Plan:

1. Add a per-server env map to ReasonixConfig (mcpEnv: { github: { ... } }), keyed off the name= prefix.
2. Pipe it into StdioTransport({ env }) at bridge time.
3. After mcp install, prompt for any requiredEnv and persist immediately.
4. On auth-shaped tool errors, surface a one-liner pointing at how to fix.

I'd keep command / args frozen for catalog-installed servers and only allow editing for hand-written spec strings — that way the catalog stays a known-good corpus. Manual specs are already fully user-controlled today.

Will pick this up. Happy to take a PR on (1)+(2) if you want it; (3) and (4) can land separately.