fix(workspace): permission enforcement, invite auto-create, switch clears stores

- DeleteAgent: require owner/admin role (was member-only check)
- ListAgentTasks: add workspace membership verification (was unauthenticated)
- CreateMember: auto-create user if email not found (enables invite flow)
- Workspace switch: clear issue/inbox/agent stores before hydrating new data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/features/workspace/store.ts

@@ -2,6 +2,7 @@
 
 import { create } from "zustand";
 import type { Workspace, MemberWithUser, Agent } from "@multica/types";
+import { useIssueStore, useInboxStore, useAgentStore } from "@multica/store";
 import { api } from "@/shared/api";
 
 interface WorkspaceState {
@@ -76,6 +77,11 @@ export const useWorkspaceStore = create<WorkspaceStore>((set, get) => ({
     const ws = workspaces.find((item) => item.id === workspaceId);
     if (!ws) return;
 
+    // Clear stale data from other stores before switching
+    useIssueStore.getState().setIssues([]);
+    useInboxStore.getState().setItems([]);
+    useAgentStore.getState().setAgents([]);
+
     await hydrateWorkspace(workspaces, ws.id);
   },