feat(app-instance): 集成Beaver后端并更新配置管理

集成新的Beaver后端服务到应用实例中，替换原有的nanobot实现。

主要变更包括：
- 在Dockerfile和环境配置中添加Beaver相关路径和配置变量
- 更新工作目录结构从.nanobot到.beaver
- 实现Beaver引擎加载器，支持配置文件加载和工具组装
- 添加内置工具如ListDirectoryTool、ReadFileTool、SearchFilesTool
- 更新消息处理流程，支持通道适配器和网关模式
- 重构技能系统，支持显式工具提示和嵌入式检索
- 改进错误处理和生命周期管理

此变更使应用实例能够使用统一的Beaver后端进行AI代理运行时管理。

app-instance/backend/beaver/interfaces/channels/manager.py

@@ -0,0 +1,76 @@
+"""Channel manager for routing gateway outbound messages."""
+
+from __future__ import annotations
+
+import asyncio
+from contextlib import suppress
+
+from beaver.foundation.events import MessageBus, OutboundMessage
+
+from .base import ChannelAdapter
+
+
+class ChannelManager:
+    """Start/stop channel adapters and dispatch outbound messages to them."""
+
+    def __init__(self, bus: MessageBus) -> None:
+        self.bus = bus
+        self.channels: dict[str, ChannelAdapter] = {}
+        self.undeliverable: list[OutboundMessage] = []
+        self.started = False
+
+    def register(self, channel: ChannelAdapter) -> None:
+        if self.started:
+            raise RuntimeError("Cannot register channels after ChannelManager.start()")
+        if channel.name in self.channels:
+            raise ValueError(f"Channel already registered: {channel.name}")
+        if channel.bus is not self.bus:
+            raise ValueError("Channel must share the same MessageBus as ChannelManager")
+        self.channels[channel.name] = channel
+
+    async def start(self) -> None:
+        started: list[ChannelAdapter] = []
+        try:
+            for channel in self.channels.values():
+                await channel.start()
+                started.append(channel)
+        except BaseException:
+            for channel in reversed(started):
+                with suppress(BaseException):
+                    await channel.stop()
+            raise
+        else:
+            self.started = True
+
+    async def stop(self) -> None:
+        errors: list[BaseException] = []
+        for channel in reversed(tuple(self.channels.values())):
+            try:
+                await channel.stop()
+            except Exception as exc:  # pragma: no cover - defensive cleanup path
+                errors.append(exc)
+        self.started = False
+        if errors:
+            raise RuntimeError(f"Failed to stop {len(errors)} channel(s)") from errors[0]
+
+    async def dispatch_outbound(self, stop_event: asyncio.Event) -> None:
+        """Route bus outbound messages until stopped and the queue is drained."""
+
+        while True:
+            if stop_event.is_set() and self.bus.outbound_size == 0:
+                break
+
+            try:
+                message = await asyncio.wait_for(self.bus.consume_outbound(), timeout=0.25)
+            except asyncio.TimeoutError:
+                continue
+
+            channel = self.channels.get(message.channel)
+            if channel is None:
+                self.undeliverable.append(message)
+                continue
+
+            try:
+                await channel.send(message)
+            except Exception:  # pragma: no cover - defensive channel isolation
+                self.undeliverable.append(message)