Rebrand header: rename product to "KITT KI HUB" and separate team identity from product identity

## Problem

The current header displays the KITT emblem next to the text "KI HUB", giving roughly equal visual prominence to the team brand (KITT) and the product name. This creates ambiguity: visitors see a team logo as part of the product identity, with no clear hierarchy.

This is a tracked follow-up to #93, which introduced the current KITT emblem in the header. The intent here is to revisit that approach and establish a clearer product vs. team separation.

> **Reference screenshot:** *(see attached image — if not embedded, added manually)*

## Proposed solution

### Product name
Rename the product to **KITT KI HUB** — combining the team prefix with the product name into a single, unified brand. This preserves the KITT identity while making it part of the product brand, not a competing visual element.

### Header
- Display **KITT KI HUB** as the primary product name (typographic, no emblem or with a minimal wordmark)
- Remove or significantly reduce the KITT emblem from the header
- The product name should be immediately readable as the first thing a visitor perceives

### Footer
- Keep the KITT emblem in the footer as the team attribution (already present in `PageFrame.astro`)
- Optionally add a "Built by KITT · Digdir" line to make the team attribution explicit

## Files likely affected

- `website/src/components/Header.astro` (lines 27–32) — logo + brand text
- `website/src/components/PageFrame.astro` (lines 46–51) — footer brand block
- `website/public/images/kitt-emblem.svg` — may need a product-level wordmark as a new asset

## Acceptance criteria

- [ ] The header shows **KITT KI HUB** as the product name with clear typographic prominence
- [ ] The KITT emblem is absent from or clearly secondary in the header
- [ ] The KITT emblem remains in the footer as team attribution
- [ ] A new or returning user can immediately identify "KITT KI HUB" as the product name
- [ ] Renders correctly on desktop and mobile
- [ ] Passes CI: `npm run build && npm run plugin:validate`