Surface the "Not Installed" Alert After a Registry Import

[jbouder]

Summary

A workspace imported from a registry lands with install_status: 'not_installed' — the environment still has to be installed before the workspace is usable. But handleImport in frontend/src/pages/Registries.tsx navigates to /workspaces on success, so the user never sees the not-installed alert on the workspace detail page. Navigate to the newly imported workspace's detail view instead, and confirm the alert renders for the import path.

Motivation

• Registry import has exactly the same post-create gap as workspace creation: a workspace that exists but can't be used until the environment is installed
• install_status is derived server-side from on-disk state (internal/service/workspace_env.go), so an imported workspace already reports not_installed — no backend or API work needed
• registriesApi.importEnvironment already returns the created Workspace, so its id is in hand for the redirect
• Landing on the list page after import gives no next-step signal; landing on the detail page puts the alert and the Install action directly in front of the user
• Confirms the alert is state-driven rather than tied to one creation path

Acceptance Criteria

• On successful import, handleImport navigates to the new workspace's detail route (/workspaces/:id) using the id from the importEnvironment response, instead of /workspaces
• If the response has no usable id, the current /workspaces navigation is kept as a fallback rather than erroring
• The not-installed alert renders on that detail page for an imported workspace, with no import-specific branching in the alert's condition
• The import panel still closes and the workspaces/jobs queries are still invalidated (existing useImportEnvironment onSuccess behavior unchanged)
• Import failures continue to show the inline error in the panel and do not navigate
• Tests cover: successful import navigates to the new workspace detail route, and the alert is present there for a not_installed workspace
• pnpm test and biome check pass with no new warnings

Out of Scope

• Building the alert itself — that lands in the workspace-creation alert issue; this one only makes the import path reach it
• Auto-triggering an install as part of import
• Any change to the import API, its response shape, or install_status derivation
• Surfacing install state on the workspaces list page (pages/Workspaces.tsx) — InstallControls already gives each row an action
• The other registries browse-table fixes (duplicate Import button, row border, collapse, tag default)