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Description

## Parent Epic: #195

## Description
Integrate the app system with the existing tool registry so apps can be used in workflows.

## Location
engine/apps/tool_bridge.py, engine/tools/registry.py

## Tool Name Convention
apps.{app_name}.{action_name}

Examples:
- apps.slack.send_message
- apps.github.create_issue
- apps.email.send

## AppToolBridge Class

### register_app_tools(app_id, version_id, tenant_id)
For each action in app:
1. Create wrapper function
2. Register with tool registry
3. Set waits_for_event flag

### unregister_app_tools(app_id, tenant_id)
Remove app tools from registry when uninstalled

### create_tool_wrapper(app_id, version_id, action_name)
Returns function with signature:
def wrapper(ctx: DurableContext, **kwargs) -> Any:
    return app_executor.execute(
        ctx=ctx,
        app_id=app_id,
        version_id=version_id,
        action_name=action_name,
        tenant_id=ctx.tenant_id,
        kwargs=kwargs,
    )

## Tool Registry Updates

### Tenant-Scoped Tool Registration
Apps are tenant-scoped, so tool registry needs tenant awareness.

Option 1: Prefix tools with tenant
- tools.{tenant_id}.apps.slack.send_message
- Requires tenant context in tool lookup

Option 2: Dynamic lookup
- Keep tool name as apps.slack.send_message
- Lookup tenant installation at execution time
- Fail if app not installed for tenant

Recommended: Option 2 (cleaner, runtime check)

### registry.py Changes
- Add is_app_tool(name) method
- Add get_app_executor() method
- Modify get() to handle app tools specially

## Workflow Usage
```python
builder.task(
    'notify',
    'apps.slack.send_message',
    kwargs={'channel': '#alerts', 'message': 'Hello'}
)
```

## Lazy Loading
App tools loaded on first use, not at worker startup

## Testing
- Test tool registration
- Test tool execution through registry
- Test tenant isolation
- Test unregistration on uninstall

Due Date (YYYY-MM-DD)

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Edit Issue #204