fix(cli): gate mcp-dev-wrapper debug stderr behind env flag

[smorchj]

Closes #15

Summary

mcp-dev-wrapper currently writes hot-reload notices, the SSE log-server banner, and per-restart messages to stderr unconditionally. That's noisy when debugging stdio MCP, where stderr is the only signal channel you actually want to read.

This PR gates all informational logs behind an env flag while keeping real failures unconditional.

Changes

Single file: typescript/packages/cli/src/mcp-dev-wrapper.ts

1. Add a DEBUG_ENABLED constant computed once at module load:

const DEBUG_ENABLED = !!(
  process.env.NITROSTACK_DEBUG ||
  /(^|,)nitrostack(:|,|$)/.test(process.env.DEBUG ?? '')
);

Both forms are supported so users coming from the broader Node ecosystem can use the standard DEBUG=nitrostack pattern, while NITROSTACK_DEBUG=1 is the canonical short form.

2. Add a debug(...args) helper that routes through console.error only when the flag is set.

3. Replace 10 informational console.error calls with debug():

   • Log streaming server running at ... banner
   • MCP_SERVER_PORT is ... debug line
   • Server exited with code N (attempt N/M), restarting... (non-fatal restart)
   • Server exited with code N, restarting... (clean exit)
   • Changes detected, restarting server...
   • Server restarted successfully
   • File changed: ...
   • File added: ...
   • Shutting down...

4. Keep these on unconditional console.error:

   • Usage line when distPath is missing
   • Server failed N times in a row. Giving up. (consecutive-failure bail-out)
   • Server error: ... from mcpProcess.on('error')
   • Unhandled rejection in run().catch()

Testing

• npm run build passes with no TypeScript errors
• Verified the compiled output: 6 unconditional console.error calls remain (real failures), 10 calls now route through debug()
• With NITROSTACK_DEBUG=1 set, behavior is identical to before
• With the flag unset, stderr only carries actual failures

Acceptance criteria

• Debug lines (e.g. MCP_SERVER_PORT) behind NITROSTACK_DEBUG or DEBUG namespace
• Real failures remain obvious on stderr