feat(agents): Phase 6 tool system refactoring

Phase 6.1: ToolRegistry infrastructure
- Add ToolManifest with ToolCategory, PermissionClass, SideEffectScope
- Add ToolRegistry singleton with register/get/unregister/list/search
- Add BaseTool abstract class with ReadTool/WriteTool/DBWriteTool/ExternalTool/NetworkTool subclasses
- Add migration layer for backward compatibility

Phase 6.2: Hook interception system
- Add HookType (PRE_TOOL_USE, POST_TOOL_USE, TOOL_ERROR, TOOL_SKIP)
- Add HookManager with singleton for hook registration
- Add HookExecutor for pre/post/error hook execution

Phase 6.3: Streaming execution
- Add StreamingToolExecutor with batch execution support

Phase 6.4: New builtin tools
- Add file_tools: GlobTool, GrepTool, ReadFileTool, WriteFileTool
- Add system_tools: BashTool, PowerShellTool
- Add dev_tools: LSPTools, GitTool
- Add collaboration_tools: TeamAgentTool, TaskBroadcastTool

Tests: 29 passed

backend/app/agents/tools/hooks/__init__.py

@@ -0,0 +1,46 @@
+"""Hook 系统 - Phase 6.2"""
+
+from app.agents.tools.hooks.types import (
+    HookDefinition,
+    HookResult,
+    HookStage,
+    HookTrigger,
+    HookType,
+    ExecutionContext,
+    HookHandler,
+    PreToolHook,
+    PostToolHook,
+    ErrorToolHook,
+    SkipToolHook,
+)
+from app.agents.tools.hooks.manager import (
+    HookManager,
+    get_hook_manager,
+    reset_hook_manager,
+)
+from app.agents.tools.hooks.executor import (
+    HookExecutor,
+    get_hook_executor,
+)
+
+__all__ = [
+    # Types
+    "HookType",
+    "HookStage",
+    "HookTrigger",
+    "HookDefinition",
+    "HookResult",
+    "ExecutionContext",
+    "HookHandler",
+    "PreToolHook",
+    "PostToolHook",
+    "ErrorToolHook",
+    "SkipToolHook",
+    # Manager
+    "HookManager",
+    "get_hook_manager",
+    "reset_hook_manager",
+    # Executor
+    "HookExecutor",
+    "get_hook_executor",
+]