feat: implement agentic and workflow execution modes with correspondi…

[yaonyan]

This pull request introduces a major refactor to the execution mode system for the MCP compose server, moving from hardcoded handling of agentic and workflow modes to a flexible plugin-based architecture. Execution modes are now implemented as plugins, allowing for easier extensibility and customization. The changes include new plugin hooks, type updates, and the registration of built-in mode plugins.

Plugin System Refactor (most important):

• Added a new registerAgentTool hook to the ToolPlugin interface, enabling plugins to register custom agent tool implementations for different execution modes.
• Refactored the server to trigger the registerAgentTool plugin hook instead of directly registering agentic or workflow tools; throws an error if no plugin handles the mode.
• Implemented built-in plugins for "agentic" and "agentic_workflow" modes, replacing previous direct registration logic. (mode-agentic-plugin.ts, mode-workflow-plugin.ts) [1] [2] [3] [4]

Type System Improvements:

• Updated all relevant types and interfaces to use the new ExecutionMode type instead of string literals for mode selection. [1] [2] [3] [4] [5] [6] [7] [8]

Plugin Utility and Manager Enhancements:

• Modified plugin application logic to match modes exactly and added support for the new hook in plugin validation. [1] [2]
• Added triggerRegisterAgentTool method to the PluginManager for handling agent tool registration via plugins.

Exports and Imports:

• Updated module exports to include new plugin types and built-in plugins in mod.ts and built-in/index.ts. [1] [2]

Minor Fixes and Improvements:

• Passed toolName to planning prompts in AgenticExecutor to improve context. [1] [2]