Phase 11: remote UX & network attach (0.11.0)

- Live remote-stack logs over a WebSocket proxied through the central app to
  the agent (/ws/agent-logs/{agent}/{stack}); agent gains a WS log endpoint.
- Deploy to a remote host from the UI: host selector in the New Stack editor
  and template dialog; templates instantiate onto an agent via the proxy.
- Network attach/detach: expandable inspect view per network with
  connect/disconnect + container picker; GET /{id}/containers, POST connect/disconnect.
- Remove dead pages/Placeholder.tsx.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/routers/templates.py

@@ -8,10 +8,12 @@ from sqlmodel import Session
 
 from auth import get_current_user, require_admin
 from database import get_session
+from models.agent import Agent
 from models.stack import Stack
 from models.template import TemplateInstantiateRequest, TemplateSaveRequest
 from models.user import User
-from services import audit_service, compose_service, template_service
+from services import agent_service, audit_service, compose_service, template_service
+from services.agent_service import AgentError
 
 router = APIRouter(prefix="/api/templates", tags=["templates"])
 
@@ -72,7 +74,7 @@ def delete_template(
 
 
 @router.post("/{template_id}/instantiate", status_code=201)
-def instantiate(
+async def instantiate(
     template_id: str,
     body: TemplateInstantiateRequest,
     request: Request,
@@ -83,11 +85,32 @@ def instantiate(
     if not tpl:
         raise HTTPException(status_code=404, detail="Template not found")
 
+    rendered = template_service.render(tpl["yaml"], body.values)
+
+    if body.agent_id is not None:
+        agent = session.get(Agent, body.agent_id)
+        if not agent:
+            raise HTTPException(status_code=404, detail=f"Agent {body.agent_id} not found")
+        try:
+            result = await agent_service.call(
+                session, agent, "POST", "/agent/stacks",
+                json={"name": body.name, "yaml": rendered, "env": None},
+            )
+        except AgentError as exc:
+            raise HTTPException(
+                status_code=exc.status if exc.status >= 400 else 502,
+                detail={"error": exc.error, "detail": exc.detail},
+            )
+        audit_service.record(
+            session, user=user.username, action="template.instantiate",
+            target=f"{agent.name}/{result.get('id')}", detail=template_id, ip=_ip(request),
+        )
+        return {"id": result.get("id"), "name": body.name, "agent_id": agent.id}
+
     stack_id = compose_service.slugify(body.name)
     if session.get(Stack, stack_id) or os.path.isdir(compose_service.stack_dir(stack_id)):
         raise HTTPException(status_code=409, detail=f"Stack '{stack_id}' already exists")
 
-    rendered = template_service.render(tpl["yaml"], body.values)
     compose_service.write_compose(stack_id, rendered)
     stack = Stack(id=stack_id, name=body.name, description=tpl.get("description"))
     session.add(stack)
@@ -96,4 +119,4 @@ def instantiate(
         session, user=user.username, action="template.instantiate",
         target=stack_id, detail=template_id, ip=_ip(request),
     )
-    return {"id": stack_id, "name": body.name}
+    return {"id": stack_id, "name": body.name, "agent_id": None}