Support sessions_spawn(...) stdout protocol for external evolution engines integration

## Problem

QwenPaw currently cannot integrate with external evolution engines like [Evolver](https://github.com/EvoMap/evolver) due to two limitations:

1. **Cron system only supports \`text\` and \`agent\` task types** - \`shell\` type is not supported, preventing users from scheduling shell-based tools
2. **No stdout protocol pickup** - QwenPaw doesn't understand the \`sessions_spawn(...)\` protocol that Evolver (and potentially other tools) emit to stdout

## Background

Evolver is a popular GEP-powered self-evolution engine for AI agents. It integrates with agent runtimes by:

1. Scanning logs and memory for patterns
2. Generating evolution prompts
3. Emitting \`sessions_spawn(...)\` directives to stdout
4. The host runtime picks up these directives and executes follow-up actions

This design works seamlessly with [OpenClaw](https://openclaw.com), which interprets the \`sessions_spawn(...)\` protocol automatically. However, QwenPaw has no mechanism to capture and act on such stdout output.

## Current State

When trying to integrate Evolver with QwenPaw:
- Users cannot create cron jobs for Evolver's auto_consumer script (\`task_type: shell\` is rejected)
- Even if manually executed, QwenPaw doesn't pick up the \`sessions_spawn(...)\` output
- Evolution loop is broken - no automatic follow-up actions

## Proposed Solution

Add support for the \`sessions_spawn(...)\` stdout protocol:

1. **stdout pickup mechanism**: When external tools emit \`sessions_spawn(...)\` to stdout, QwenPaw should capture it and trigger corresponding actions (e.g., spawn a new session, apply a skill, etc.)

2. **Protocol definition**:
\`\`\`
sessions_spawn(action_type, payload)
\`\`\`
Where \`action_type\` could be \`apply_skill\`, \`update_memory\`, \`spawn_agent\`, etc.

3. **Optional: shell cron support**: Consider adding \`shell\` task type with proper security constraints (whitelist directories, allowed commands, etc.)

## Benefits

1. **External evolution engine integration** - QwenPaw can integrate with Evolver and similar tools
2. **Self-evolution capability** - Users get auditable, automatic agent improvement
3. **Protocol standardization** - \`sessions_spawn(...)\` could become a standard for agent-tool communication
4. **Competitive parity** - Hermes Agent already has built-in self-evolution via [agentskills.io](https://agentskills.io)

## Related

- Evolver README mentions OpenClaw integration: https://github.com/EvoMap/evolver#platform-integration
- Similar discussion in Hermes Agent: https://github.com/NousResearch/hermes-agent (agentskills.io standard)

## Alternative Considered

I also considered asking Evolver to adapt to QwenPaw's architecture, but:
- Evolver's stdout protocol design is clean and protocol-constrained
- It's easier for QwenPaw to implement stdout pickup than for Evolver to change its core architecture
- This protocol could benefit multiple external tools, not just Evolver

---

Would the team consider adding this capability? I'm happy to contribute to the design or implementation if needed.