refactor(cleanup): remove legacy agent classes and complete EvoAgent migration

Remove deprecated AnalystAgent, PMAgent, and RiskAgent classes.
All agent creation now goes through UnifiedAgentFactory creating EvoAgent instances.

- Delete backend/agents/analyst.py (169 lines)
- Delete backend/agents/portfolio_manager.py (420 lines)
- Delete backend/agents/risk_manager.py (139 lines)
- Update all imports to use EvoAgent exclusively
- Clean up unused imports across 25 files
- Update tests to work with simplified agent structure

Constraint: EvoAgent is now the single source of truth for all agent roles
Constraint: UnifiedAgentFactory handles runtime agent creation
Rejected: Keep legacy aliases | creates maintenance burden
Confidence: high
Scope-risk: moderate (affects agent instantiation paths)
Directive: All new agent features must be added to EvoAgent, not legacy classes
Not-tested: Kubernetes sandbox executor (marked with TODO)

backend/agents/__init__.py

@@ -1,48 +1,46 @@
 # -*- coding: utf-8 -*-
 """
-Agents package for the current mixed runtime.
+Agents package for the EvoAgent-based runtime.
 
 Exports:
-- EvoAgent: Next-generation agent with workspace support
+- EvoAgent: Core agent with workspace support
 - ToolGuardMixin: Tool call approval/denial flow
 - CommandHandler: System command handling
 - AgentFactory: Design-time agent creation under `workspaces/`
-- WorkspaceManager: Legacy alias for the persistent `workspaces/` registry
+- WorkspaceManager: Alias for the persistent `workspaces/` registry
 - WorkspaceRegistry: Explicit design-time `workspaces/` registry
 - RunWorkspaceManager: Run-scoped workspace asset manager
 - AgentRegistry: Central agent registry
-- Legacy compatibility: AnalystAgent, PMAgent, RiskAgent
+- UnifiedAgentFactory: Runtime agent factory for creating EvoAgent instances
 """
 
-# New EvoAgent architecture (from agent_core.py)
+# EvoAgent architecture
 from .agent_core import EvoAgent, ToolGuardMixin, CommandHandler
 from .factory import AgentFactory, ModelConfig
+from .unified_factory import UnifiedAgentFactory, get_agent_factory, clear_factory_cache
 from .workspace import WorkspaceManager, WorkspaceRegistry, WorkspaceConfig
 from .workspace_manager import RunWorkspaceManager
 from .registry import AgentRegistry, AgentInfo, get_registry, reset_registry
 
-# Legacy agents (backward compatibility)
-from .analyst import AnalystAgent
-from .portfolio_manager import PMAgent
-from .risk_manager import RiskAgent
-
 __all__ = [
-    # New architecture
+    # Core EvoAgent
     "EvoAgent",
     "ToolGuardMixin",
     "CommandHandler",
+    # Factories
     "AgentFactory",
     "ModelConfig",
+    "UnifiedAgentFactory",
+    "get_agent_factory",
+    "clear_factory_cache",
+    # Workspace
     "WorkspaceManager",
     "WorkspaceRegistry",
     "WorkspaceConfig",
     "RunWorkspaceManager",
+    # Registry
     "AgentRegistry",
     "AgentInfo",
     "get_registry",
     "reset_registry",
-    # Legacy compatibility
-    "AnalystAgent",
-    "PMAgent",
-    "RiskAgent",
 ]