feat: Implement AgentFlow event-driven workflows with CLI support

Add complete AgentFlow implementation for trigger-based workflows:

Core Implementation:
- AgentFlow type definitions in aof-core (trigger, nodes, connections)
- AgentFlowExecutor runtime with state management and event handling
- Variable interpolation (${event.*}, ${node-id.*}) support
- Conditional routing with 'when' expressions

CLI Commands:
- `aofctl run flow` - Execute AgentFlow configs with mock input
- `aofctl describe flow` - Display flow structure and configuration
- Auto-detection of AgentFlow vs Workflow based on YAML 'kind' field

Examples & Guides:
- Slack K8s bot agent and flow examples
- Slack app setup guide
- Complete Slack bot tutorial

Documentation Updates:
- Updated AgentFlow spec reference with all trigger/node types
- Updated schemas, concepts, getting-started docs
- Marked AgentFlow phases 1-3 as implemented in design doc
- Added flow commands to CLI reference

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: initcron

CLAUDE.md

@@ -502,3 +502,4 @@ NEVER create files unless they're absolutely necessary for achieving your goal.
 ALWAYS prefer editing an existing file to creating a new one.
 NEVER proactively create documentation files (*.md) or README files. Only create documentation files if explicitly requested by the User.
 Never save working files, text/mds and tests to the root folder.
+- Strictly follow kubectl style implementation for aofctl. For example use "aofctl run agent" instead of "aofctl agent run". If you find anything non compliant, correct it.