Add local Streams development support and stream browser improvements

[sorenbs]

Summary

• add local Streams development wiring and streams-only demo/runtime support
• add the stream event view improvements: search, follow modes, URL state, aggregation strip, diagnostics, and long-poll integration
• add a resizable Studio sidebar so long stream names can be revealed without changing layout code

Verification

• pnpm exec vitest run demo/ppg-dev/runtime-options.test.ts demo/ppg-dev/runtime.test.ts demo/ppg-dev/DemoShell.test.ts demo/ppg-dev/shutdown.test.ts ui/hooks/use-stream-details.test.tsx ui/hooks/use-stream-events.test.tsx ui/studio/views/stream/StreamView.test.tsx ui/studio/Navigation.test.tsx ui/studio/Studio.test.tsx
• pnpm exec vitest run ui/studio/context.test.tsx ui/studio/Navigation.test.tsx ui/studio/Studio.test.tsx
• pnpm typecheck
• Playwright validation on http://localhost:4310