MCP server skip should be WARNING, not ERROR in /doctor output

Description

When running /reload-plugins, if an MCP server is skipped (e.g., unavailable or not configured), it reports as an error:

Reloaded: 2 plugins · 6 skills · 5 agents · 0 hooks · 4 plugin MCP servers · 0 plugin LSP servers
1 error during load. Run /doctor for details.

Running /doctor then surfaces this as an error-level diagnostic.

Expected Behavior

Skipped MCP servers should be classified as warnings, not errors. An MCP server being unavailable or intentionally skipped is not a critical failure — treating it as an error creates unnecessary noise and makes it harder to distinguish actual problems in /doctor output.

Suggested Fix

Downgrade MCP server skip/unavailable events from ERROR to WARNING severity in the /doctor diagnostics output.