[Gap]: Document drift detection and the upgrade flow for MCP servers

[danbarr]

Gap

Two user-facing surfaces of the drift mechanic added in stacklok/toolhive-studio#1604 are undocumented:

1. Upgrade-available button on server cards: when a registry-sourced server's image is newer upstream, the card renders an amber ArrowUpCircle button next to start/stop with tooltip Update available: {localTag} → {registryTag}, plus an Update to {tag} entry in the kebab menu.
2. Registry drift detection on customize-tools: when the upstream tool set changes, the customize-tools page surfaces the diff via a DriftDetails component.

Source in app (v0.30.0)

• renderer/src/features/mcp-servers/components/card-mcp-server/index.tsx:29-72 (UpdateVersionButton)
• renderer/src/features/mcp-servers/components/card-mcp-server/server-actions/items/update-version-menu-item.tsx
• renderer/src/features/mcp-servers/components/drift-details.tsx
• renderer/src/features/mcp-servers/sub-pages/customize-tools/page.tsx

Docs to update

• docs/toolhive/guides-ui/run-mcp-servers.mdx (under "Manage MCP servers")
• docs/toolhive/guides-ui/customize-tools.mdx (drift detection)

Introducing PR

stacklok/toolhive-studio#1604 — feat(workload): improve update flow and detect envs drift

Parent

Part of #751.