Fix: dev:ui missing and dev:app / dev:agent fail with "No package found with name 'app' in workspace"

[iamkalio]

Two problems in the current setup:

1. README vs scripts
   README says to use dev:ui, but only dev:app exists → pnpm run dev:ui fails with "Missing script: dev:ui".

2. Turbo filter
   Root package.json uses --filter='app' and --filter='agent', but package names are @repo/app and @repo/agent. So pnpm run dev:app (and dev:agent) fails with "No package found with name 'app' in workspace".

Fix:
In root package.json, use --filter='@repo/app' and --filter='@repo/agent' (and optionally add a dev:ui script that does the same as dev:app).
In README, we either document dev:app instead of dev:ui, or add dev:ui as above so README is correct.