feat(finder): /finder route and page

[GMNAPI]

Next.js 15 App Router route at /finder.

page.tsx (Server Component):

• Catalan <Metadata>: title + og:description optimized for conversion
• Renders <FinderWizard /> (client component)
• Minimal sticky header with LJ logo + "← Inici" link
• Intro copy: "8 preguntes per saber si pots rebre fins a 250€/mes"

Status: ✅ Implemented in web/src/app/finder/page.tsx

Effort: XS (~1h)
Deps: #28 (VerdictScreen)