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/__init__.py

@@ -1,6 +1,9 @@
 from app.agents.tools.search import (
-    search_knowledge, get_knowledge_graph_context,
-    build_knowledge_graph, hybrid_search, web_search,
+    search_knowledge,
+    get_knowledge_graph_context,
+    build_knowledge_graph,
+    hybrid_search,
+    web_search,
 )
 from app.agents.tools.task import get_tasks, create_task, update_task_status
 from app.agents.tools.forum import get_forum_posts, create_forum_post, scan_forum_for_instructions
@@ -13,6 +16,58 @@ from app.agents.tools.schedule import (
 )
 from app.agents.tools.time_reasoning import resolve_time_expression
 
+# Phase 6.1: Tool Registry exports
+from app.agents.tools.registry import (
+    ToolRegistry,
+    get_tool_registry,
+    reset_tool_registry,
+)
+from app.agents.tools.manifest import (
+    HookConfig,
+    PermissionClass,
+    SideEffectScope,
+    ToolCategory,
+    ToolManifest,
+)
+from app.agents.tools.migration import (
+    migrate_tool,
+    migrate_all_tools,
+    get_tool_executor,
+    BackwardCompatTool,
+)
+
+# Phase 6.2: Hook System exports
+from app.agents.tools.hooks import (
+    HookManager,
+    HookExecutor,
+    HookType,
+    HookDefinition,
+    HookResult,
+    ExecutionContext,
+    get_hook_manager,
+    get_hook_executor,
+)
+
+# Phase 6.3: Streaming Executor exports
+from app.agents.tools.streaming import (
+    StreamingToolExecutor,
+    get_streaming_executor,
+)
+
+# Phase 6.4: Builtin Tools exports
+from app.agents.tools.builtins import (
+    GlobTool,
+    GrepTool,
+    ReadFileTool,
+    WriteFileTool,
+    BashTool,
+    PowerShellTool,
+    LSPTools,
+    GitTool,
+    TeamAgentTool,
+    TaskBroadcastTool,
+)
+
 TASK_TOOLS = [
     get_tasks,
     create_task,