Add distributed execution support via Redis

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Problem

Currently, vulnz runs providers sequentially or with goroutine-based parallelism on a single machine. For large-scale deployments (e.g., enterprise vulnerability management pipelines), distributed execution across multiple workers would enable:

• Horizontal scaling of provider runs
• Resilience against single-node failures
• Load balancing across geographic regions

Proposed Solution

Implement distributed execution using Redis as the coordination layer:

Architecture

1. Task Queue: Redis list/streams for provider execution tasks
2. Worker Pool: Multiple vulnz instances consuming from the queue
3. Result Aggregation: Centralized storage (S3, PostgreSQL, or shared NFS)
4. Status Tracking: Redis hashes for task state (pending, running, completed, failed)

Key Components

• internal/distributed/ - New package for distributed execution
• internal/distributed/queue.go - Redis queue implementation
• internal/distributed/worker.go - Worker goroutine consuming tasks
• internal/distributed/coordinator.go - Task distribution and result collection

Configuration

executor:
  mode: distributed
  distributed:
    redis_url: "redis://localhost:6379/0"
    worker_id: "worker-1"
    result_store: "s3"
    s3:
      bucket: "vulnz-results"
      region: "eu-west-1"

Acceptance Criteria

• Redis queue implementation for task distribution
• Worker mode that consumes and executes providers
• Result aggregation to centralized storage
• Status tracking visible via vulnz status command
• Graceful shutdown and task re-queueing on worker failure
• Tests with Redis testcontainers or mock

Additional Context

This is a larger feature that would significantly enhance vulnz for enterprise deployments. The single-machine executor (internal/provider/executor.go) should remain as the default mode.

Labels: enhancement, help wanted