[S1][frontend] Picker UI: moment + guide cards + Tailwind base

[d3v07]

Scope

Build the entry screen — recipient/occasion/form picker and the guide card list. No backend hookup yet; consume static guide stubs handed off by Frex22 (S1-persona).

Acceptance

• app/page.tsx renders the moment-picker (recipient, occasion, form)
• components/GuidePicker.tsx renders cards from a typed Guide[] prop
• Tailwind theme tokens set: serif body for artifact view, sans for chrome — pick a non-default font pair (no Inter)
• Color palette derived from the design (warm, low-key); no purple→blue gradient
• Selected Session (recipient/occasion/form/guide_id) persists to localStorage

Out of scope

Streaming chat shell (Sprint 2), drafting view (Sprint 3).

Branch

feat/sprint-1-picker-ui off persona-core-dev.