docs: add Workspaces documentation across Cloud, Interface, and Subscription pages

[lin-bot23]

Summary

Adds Workspaces documentation across multiple sections of the docs, covering the complete workspace feature set in Comfy Cloud. The workspace feature was already fully implemented in the frontend UI (src/platform/workspace/) but had no corresponding documentation.

Changes

New pages

• cloud/workspace.mdx (en/zh/ja) — Complete Workspaces reference page covering:
  • Overview of Personal vs Team workspaces
  • Creating a team workspace (step-by-step)
  • Workspace roles (owner vs member) and their permissions
  • Managing members (invite, remove, revoke invitations)
  • Invite limits and subscription requirements
  • Workspace settings (rename, delete, leave)
  • Switching between workspaces
  • Billing and subscription per workspace
  • URL shortcut parameters (?create_workspace=1, ?invite=TOKEN)
  • FAQ section

Updated pages

• get_started/cloud.mdx (en/zh/ja) — Added "Team collaboration" card to Key features, Workspace link card near pricing section
• interface/overview.mdx — Added Tip linking to Workspaces documentation
• support/subscription/managing.mdx — Added "Personal vs Team workspace subscriptions" section
• docs.json — Registered cloud/workspace in navigation for all 3 languages

Info sources

All content derived from the frontend source code at src/platform/workspace/:

• teamWorkspaceStore.ts (MAX_OWNED_WORKSPACES = 10, MAX_WORKSPACE_MEMBERS = 50)
• useWorkspaceUI.ts (permission matrix for owner/member/personal roles)
• Dialog components (create, invite, member management, subscription, delete)
• Invite URL loader and create workspace URL loader composables
• WorkspaceAuthGate (initialization flow)

Checklist

• English, Chinese, and Japanese versions
• No screenshots yet (can be added in a follow-up)