Allow configuring MCP slow-connection warning threshold

[richardpowellus]

Describe the feature or problem you'd like to solve

MCP servers that require authentication handshakes (e.g., OAuth, Entra ID) routinely take 5-10 seconds to connect. The CLI displays a warning for each server that exceeds the hardcoded 10-second threshold:

! MCP server 'server-a' is taking longer than expected to connect.
! MCP server 'server-b' is taking longer than expected to connect.
! MCP server 'server-c' is taking longer than expected to connect.

All servers connect successfully -- the warnings are purely cosmetic. With many MCP servers configured, startup is dominated by a wall of yellow warnings that adds noise without actionable information.

The timeout field in mcp-config.json controls the hard connection timeout (how long before giving up), but there is no way to control the warning threshold.

Proposed solution

Add support for a slowConnectionThresholdMs field in mcp-config.json, either:

Per-server (preferred):

{
  "mcpServers": {
    "my-server": {
      "type": "stdio",
      "command": "my-mcp-server",
      "args": ["start"],
      "timeout": 60000,
      "slowConnectionThresholdMs": 30000
    }
  }
}

Or globally:

{
  "mcpServers": { "...": "..." },
  "slowConnectionThresholdMs": 30000
}

The internal plumbing already supports this -- the slow-connection monitor class constructor accepts slowConnectionThresholdMs as an option, it's just not wired to any user-facing config.

Example prompts or workflows

1. User configures multiple MCP servers that authenticate via OAuth or similar
2. Each server takes ~5-10s to complete auth + upstream connect
3. User sets "slowConnectionThresholdMs": 30000 to suppress warnings for expected auth latency
4. Startup shows clean output with no false-positive warnings

Additional context

• The slow-connection monitor class already accepts slowConnectionThresholdMs in its constructor options -- this is a config-wiring change, not a new feature
• The default 10s threshold is hardcoded as a constant
• This primarily affects users with authenticated MCP proxies (OAuth servers, enterprise auth flows)
• A single OAuth/auth handshake can take ~5s, so even one hop can approach the 10s threshold