feat(beaver): 完成Task Team功能v1实现，重构后端架构支持统一内核

新增内部Task系统，包括验证、反馈门控机制，实现自动质量验证
(通过率>=0.75)和用户反馈闭环(satisfied/revise/abandon)。

实现Agent Team v1协调器，支持sequence/parallel/dag执行策略，
sub-agent复用主AgentLoop，每个run使用独立memory snapshot。

建立Skill学习pipeline，包含draft/审核/发布/回滚完整生命周期，
通过Task验证通过且用户满意才生成学习候选。

重构目录结构，移除third_party依赖，建立统一engine内核，
所有agent共享运行时基础组件。

更新ContextBuilder清理provider消息字段，增强SkillContext版本管理，
集成TaskExecutionPlanner和TaskSkillResolver实现技能解析机制。

app-instance/backend/tests/unit/test_agent_registry_resolver.py

@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+from beaver.coordinator.models import AgentDescriptor, ExecutionGraph, ExecutionNode
+from beaver.coordinator.registry import AgentRegistry, RegisteredAgent, TargetResolver
+from beaver.tasks import TaskRecord
+
+
+def _task() -> TaskRecord:
+    return TaskRecord(
+        task_id="task-1",
+        session_id="session-1",
+        description="implement tests",
+        goal="implement tests",
+        constraints=[],
+        priority=0,
+        status="open",
+        creator="test",
+        created_at="now",
+        updated_at="now",
+    )
+
+
+def test_registry_seeds_builtin_agents_and_filters_disabled(tmp_path) -> None:
+    registry = AgentRegistry(tmp_path)
+
+    assert {agent.agent_id for agent in registry.list_active_agents()} >= {
+        "researcher",
+        "implementer",
+        "reviewer",
+        "tester",
+        "documenter",
+    }
+
+    registry.disable_agent("tester")
+
+    assert "tester" not in {agent.agent_id for agent in registry.list_active_agents()}
+
+
+def test_resolver_selects_registered_agent_by_role_and_capabilities(tmp_path) -> None:
+    registry = AgentRegistry(tmp_path)
+    registry.upsert_agent(
+        RegisteredAgent(
+            agent_id="security-reviewer",
+            name="security-reviewer",
+            display_name="Security Reviewer",
+            role="security review",
+            description="Reviews auth, permissions, and data exposure risk.",
+            system_prompt="review security",
+            capabilities=["security", "review", "auth"],
+            priority=90,
+        )
+    )
+    resolver = TargetResolver(registry)
+    graph = ExecutionGraph(
+        strategy="sequence",
+        nodes=[
+            ExecutionNode(
+                node_id="review",
+                task="review auth handling",
+                agent=AgentDescriptor(
+                    name="reviewer",
+                    role="security review",
+                    metadata={"requested_capabilities": ["security"]},
+                ),
+            )
+        ],
+    )
+
+    resolved, reports = resolver.resolve_graph(graph, task=_task(), user_message="review auth", attempt_index=1)
+
+    assert resolved.nodes[0].agent.metadata["agent_id"] == "security-reviewer"
+    assert reports[0].fallback_used is False
+    assert reports[0].selected_agent_id == "security-reviewer"
+
+
+def test_resolver_falls_back_to_ephemeral_agent_when_no_match(tmp_path) -> None:
+    registry = AgentRegistry(tmp_path)
+    for agent in registry.list_agents():
+        registry.disable_agent(agent.agent_id)
+    resolver = TargetResolver(registry)
+    graph = ExecutionGraph(
+        strategy="sequence",
+        nodes=[ExecutionNode("rare", "rare work", AgentDescriptor(name="rare", role="rare"))],
+    )
+
+    resolved, reports = resolver.resolve_graph(graph, task=_task(), user_message="rare work", attempt_index=1)
+
+    assert resolved.nodes[0].agent.name == "rare"
+    assert resolved.nodes[0].agent.metadata["resolution"] == "fallback_ephemeral"
+    assert reports[0].fallback_used is True
+