test(cli-e2e): scaffold.runtime coverage for ui:add ai (McpUiWidget) — split from #257

[rickylabs]

Context

Split out from #257 (mcp-ui-widget island, PR #550). The McpUiWidget island itself is implemented,
IMPL-EVAL PASS, and merge-ready (behind #463 per charter upstream-first). What is NOT yet built is the
gate:e2e scaffold-runtime coverage for the ui:add path — the scaffold.runtime e2e suite
(packages/cli/e2e) currently has zero ui:add coverage.

Acceptance

• deno task e2e:cli run scaffold.runtime --cleanup --format pretty covers netscript ui:add ai
  (or ui:add mcp-ui-widget) resolving and copying McpUiWidget.tsx plus its theme-seed
  registryDependency into a scaffolded Fresh app, with no generated-workspace type errors.
• Suite asserts the copied island + css land at the expected registry path and typecheck.

Notes

• Orthogonal to the fresh-ui island (framework CLI / e2e-suite work) — a WSL Codex daemon-attached
  slice, not a fresh-ui change.
• Non-blocking for the [AI-stack FB4] fresh-ui: mcp-ui-widget (themed sandboxed ui:// iframe) #257 island merge; the island ships on its own verified gates. Refs [AI-stack FB4] fresh-ui: mcp-ui-widget (themed sandboxed ui:// iframe) #257.