Edit Issue - .issue.db

Title *

Description

## Parent Epic: #195

## Description
Create the AppExecutor class that loads and executes apps.

## Location
engine/apps/executor.py, engine/apps/loader.py

## AppLoader Class

### Responsibilities
- Load app class from different entrypoint types
- Cache loaded apps (LRU with TTL)
- Validate app structure

### Entrypoint Types

1. python_module
   - Load from installed Python module
   - Config: {'module': 'path.to.module', 'class': 'ClassName'}

2. python_code
   - Load from database-stored code
   - Config: {'code_hash': 'sha256:...', 'class_name': 'MyApp'}
   - Security: Restricted execution environment

3. webhook
   - HTTP webhook for external apps
   - Config: {'url': '...', 'auth_type': 'bearer', 'auth_secret': '...'}

### Security
- Sandbox for python_code (no os, eval, exec, etc.)
- Timeout for loading
- Memory limits

## AppExecutor Class

### Constructor
- pool: ConnectionPool
- app_cache: LRUCache(maxsize=100, ttl=300)

### execute() Method
1. Load app definition (cached)
2. Verify tenant has app installed
3. Check app status == 'enabled'
4. Load tenant configuration
5. Load secrets from Vault
6. Create AppMetadata
7. Create AppContext wrapper
8. Execute action
9. Log execution to app_execution_log
10. Return result

### Error Handling
- AppNotInstalledError
- AppDisabledError
- ActionNotFoundError
- AppExecutionError
- SecretNotFoundError

### Integration Points
- Called by tool registry wrapper
- Uses absurd_client for checkpoints

## Testing
- Test each entrypoint type
- Test caching behavior
- Test error scenarios
- Test execution logging

Due Date (YYYY-MM-DD)

Tags (comma separated)

Related Issues (IDs)

Enter IDs of issues related to this one. They will be linked as 'related'.

Edit Issue #200