Add support for SigNoz backend

[nirga]

Description

Add support for SigNoz as an observability backend, enabling users to query OpenTelemetry traces from SigNoz (self-hosted or cloud).

Motivation

SigNoz is mentioned specifically in the roadmap ("Support for additional backends (SigNoz, ClickHouse)"). SigNoz is a popular open-source alternative to Datadog/New Relic with native OpenTelemetry support, making it ideal for cost-conscious teams and self-hosted deployments.

Implementation Requirements

1. Backend Implementation

• Create src/openllmetry_mcp/backends/signoz.py following the abstract interface in backends/base.py
• Implement the following methods:
  • search_traces() - Query traces using SigNoz Query Service API
  • get_trace() - Retrieve full trace details
  • list_services() - List available services
  • get_aggregated_usage() - Aggregate token usage metrics

2. Configuration

• Add signoz as a backend type option
• Required configuration:
  • BACKEND_URL: SigNoz instance URL (e.g., http://localhost:3301 or https://your-signoz-cloud.signoz.io)
  • BACKEND_API_KEY: API key (for SigNoz Cloud) or empty for self-hosted
• Update .env.example with SigNoz configuration example

3. API Integration

Reference SigNoz APIs:

• Query Service API
• Traces API endpoints
• SigNoz uses ClickHouse backend with custom query language
• Authentication: Bearer token in Authorization header (Cloud) or no auth (self-hosted)

4. Query Language

SigNoz uses a custom query builder for filtering traces. Example:

{
  "start": 1609459200000,
  "end": 1609545600000,
  "filters": {
    "items": [
      {
        "key": {"key": "serviceName", "type": "tag"},
        "value": "api",
        "op": "="
      }
    ],
    "op": "AND"
  },
  "limit": 100
}

5. OpenLLMetry Support

Ensure proper parsing of OpenLLMetry semantic conventions (gen_ai.* attributes) from SigNoz trace spans.

6. Documentation

• Add SigNoz backend configuration to README.md
• Include Claude Desktop integration example
• Document both self-hosted and SigNoz Cloud configurations
• Add troubleshooting section for common SigNoz connection issues

7. Testing

• Add unit tests in tests/backends/test_signoz.py
• Test trace querying with SigNoz query format
• Test filtering, aggregation, and pagination
• Test error handling and authentication
• Test both self-hosted and cloud scenarios

Example Configuration

Self-hosted

BACKEND_TYPE=signoz
BACKEND_URL=http://localhost:3301

SigNoz Cloud

BACKEND_TYPE=signoz
BACKEND_URL=https://your-org.signoz.io
BACKEND_API_KEY=your_api_key_here

References

• SigNoz Official Docs
• SigNoz OpenTelemetry Guide
• SigNoz API Documentation
• SigNoz GitHub
• Future Enhancements roadmap item
• Existing backend implementations: backends/jaeger.py, backends/tempo.py, backends/traceloop.py

Acceptance Criteria

• SigNoz backend implementation complete
• All abstract methods implemented
• Query builder for SigNoz filter format
• Configuration documented (self-hosted and cloud)
• Tests passing for both deployment types
• README updated with SigNoz examples
• Works with Claude Desktop integration