chore(web): use @parallelworks/ui 0.20, with the chat from @parallelworks/ui/ai

[giraffesyo]

What was wrong or missing

Studio depended on @parallelworks/ai-chat 0.5.0 and @parallelworks/ui 0.17. The chat package has moved into @parallelworks/ui as @parallelworks/ui/ai, and ui 0.20 changed how workflow forms and graphs work. Both packages also shipped their own Tailwind build, which forced Studio to manage the cascade order between them.

What changed

• Swapped @parallelworks/ai-chat for @parallelworks/ui/ai and upgraded @parallelworks/ui to ^0.20.0. ui's prebuilt stylesheet now includes the chat rules, so the separate chat stylesheet and its pw-ai-chat layer are gone. ui still emits a top-level base layer, so layers.css keeps declaring it first.
• DependencyGraphPreview now comes from @parallelworks/ui/graph, since /workflow was renamed.
• ui's workflow form and graph no longer embed the workflow parser. They call a WorkflowEngine supplied through UIProvider. Studio mounts UIProvider at the root with a loader that imports @parallelworks/workflow-parser (new dependency, ^0.6.0) on first use, so the parser stays out of the initial bundle. The form and the graph each sit in a Suspense boundary while it loads.
• Starting values are unchanged: initializeValues is called as before, with no blank-default predicate, matching 0.17's default behavior.

How it was verified

• pnpm build: web type-check and build plus the server build pass.
• pnpm test: all 217 server tests pass. Web has 52 of 53 passing. The failure, test/attachmentsCursor.test.tsx, also fails without this change on my machine (Node 26, where localStorage is undefined when src/adapter.ts loads), and CI runs Node 22.
• Ran pnpm dev and checked in headless Chromium:
  • Chat: renders the empty state, starters and composer, with no page errors.
  • Workflow graph (?embed=dag with a mocked two-job workflow): renders Build → Test.
  • Workflow form (Workflows tab with mocked collection and form endpoints, since there was no platform credential locally): renders with expressions resolved by the parser.
  • The only console errors were 503s from /api/query while the local index was loading.
• Not checked: running a workflow against the platform, or sending a chat message to a real model (no credentials in this environment).