fix: make reporting lines more concise

[bespoyasov]

Makes the onboarding agent produce slightly more concise reporting on the DoneScreen, to fit ~70 characters:

● Added `@openfeature/server-sdk`
● Added `@spotify-confidence/openfeature-server-provider-local`
● Modified `app/welcome/welcome.tsx` — subtitle driven by flag value
● Modified `app/routes/home.tsx` — server-side flag evaluation in loader
● Created `welcome-subtitle` flag with control/treatment variants