feat: add OpenTelemetry tracing

[mattpodwysocki]

Summary

Adds OpenTelemetry tracing to mcp-docs-server, consistent with the implementation in mcp-server and mcp-devkit-server.

• src/utils/tracing.ts (new) — initializeTracing(), shutdownTracing(), getTracer(), and withToolSpan(). Suppresses OTEL diagnostic output at module load time to protect MCP stdio.
• BaseTool.run() — wraps every tool execution in a tool.<name> span via withToolSpan(); sets tool.error=true attribute when a tool returns isError: true.
• src/index.ts — calls initializeTracing() on startup, shutdownTracing() on graceful exit.
• src/utils/index.ts — exports tracing utilities from @mapbox/mcp-docs-server/utils.

Tracing is a no-op by default. It activates only when OTEL_EXPORTER_OTLP_ENDPOINT or OTEL_EXPORTER_CONSOLE_ENABLED=true is set. Uses OTEL 2.x (resourceFromAttributes instead of the removed Resource class).

Test plan

• npm run build passes
• npm test — 58 tests pass (tracing is no-op in test env via VITEST guard)
• CI green

🤖 Generated with Claude Code

[zmofei]

LGTM! Clean implementation, consistent with sibling repos. One minor issue:

src/tools/BaseTool.ts — missing tool.error attribute in catch block

The try path sets span.setAttribute('tool.error', true) when result.isError, but the catch path (which also returns isError: true) doesn't set it. Since the inner catch returns rather than re-throws, withToolSpan sees a successful completion and marks the span SpanStatusCode.OK.

Validation failures and unexpected exceptions will produce spans that look successful — no tool.error attribute, status OK.

Suggested fix:

} catch (error) {
  span.setAttribute('tool.error', true);
  return {
    isError: true,
    content: [{ type: 'text', text: (error as Error).message }]
  };
}

Not blocking — can be a follow-up.