feat: Add agent workspace system and runtime management

- Add agent core modules (agent_core, factory, registry, skill_loader)
- Add runtime system for agent execution management
- Add REST API for agents, workspaces, and runtime control
- Add process supervisor for agent lifecycle management
- Add workspace template system with agent profiles
- Add frontend RuntimeView and runtime API integration
- Add per-agent skill workspaces for smoke_fullstack run
- Refactor skill system with active/installed separation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/agents/prompts/__init__.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+"""Prompt building utilities for EvoAgent.
+
+This module provides prompt construction from workspace markdown files
+with YAML frontmatter support.
+"""
+from .builder import (
+    PromptBuilder,
+    build_system_prompt_from_workspace,
+    build_bootstrap_guidance,
+    DEFAULT_SYS_PROMPT,
+)
+
+__all__ = [
+    "PromptBuilder",
+    "build_system_prompt_from_workspace",
+    "build_bootstrap_guidance",
+    "DEFAULT_SYS_PROMPT",
+]