feat(box): add startup and availability logging for sandbox tools

Log Box runtime initialization result (success with profile info, or
failure warning). Log native tool availability status at ToolManager
startup so it's immediately clear whether exec/read/write/edit tools
are registered for the LLM.

src/langbot/pkg/box/service.py

@@ -73,6 +73,10 @@ class BoxService:
             else:
                 await self.client.initialize()
             self._available = True
+            self.ap.logger.info(
+                f'LangBot Box runtime initialized: profile={self.profile.name} '
+                f'default_workspace={self.default_host_workspace or "(none)"}'
+            )
         except Exception as exc:
             self.ap.logger.warning(f'LangBot Box runtime unavailable, sandbox features disabled: {exc}')
             self._available = False