Add SSR to the existing / navigator #200

Parent

#174 (alternative homepage layout) — see design spec.

Context

`/` is currently CSR-only — the Hugo shell renders banner + mount point + `` fallback, and the Vue island fetches `/build/navigator` on mount before any cards appear. `/browse/` (issue #174) introduces full SSR: Hugo emits the banner + curation rails + page-1 grid statically, and the Vue island hydrates over the rendered DOM.

Once `/browse/` proves the SSR plumbing is stable, `/`'s navigator can adopt the same approach. The plumbing is already in place: `fetch-tutorials.ts` will write `hugo/data/browse.json`, the shared card components live at `hugo-apps/src/shared/cards/`, and the `` boundary pattern is locked.

Scope

• Hugo template for `/` adopts the same SSR shape (mirrors the card partials from `hugo/layouts/browse/_partials/`).
• `hugo-apps/src/navigator/main.ts` switches from `createApp().mount()` to `createSSRApp().mount()`.
• Card-template-parity tests extend to cover the `/` template too.
• The progress-ring animated draw-in pattern from `/browse/` is reused.

Out of scope

• Layout changes on `/`. This issue is purely a render-strategy migration, not a redesign.

When to pick this up

Trigger condition: `/browse/` SSR has been in production for at least two weeks with no hydration-mismatch incidents, AND `/` is staying as a long-term surface.