Attaches Tessera's DZI deep-zoom + multi-layer progressive-quality behavior to a Fresco viewer by id.

Tessera 0.2 is no longer a standalone viewer — it's a layer that composes onto a <Fresco.viewer>. The Fresco viewer owns the OSD instance, the nav overlay, animations, and viewport clamping; Tessera contributes:

• A DZI source provider registered with Fresco (so any .dzi manifest URL is treated as a tile pyramid)
• A multi-layer source-swap that promotes / demotes through an ordered sources list as the user zooms in and out, with hysteresis to avoid flicker around the boundaries, and a bounds-preserving swap so the user never sees a jump to home

Usage

<Fresco.viewer id="photo" src={~p"/uploads/photo-medium.jpg"} />

<Tessera.layer
  fresco_id="photo"
  sources={[
    %{url: ~p"/uploads/photo-medium.jpg", width: 1024},
    %{url: ~p"/uploads/photo-large.jpg",  width: 2560},
    %{url: ~p"/dzi/photo.dzi"}
  ]}
/>

Sources

An ordered list of low → high quality layers. Each entry is a map with:

• :url (required) — the source URL (a plain image or a .dzi manifest)
• :width (optional) — intrinsic pixel width. Tessera computes the zoom threshold past which this source is upscaled and swaps to the next one up. Omit for .dzi sources — DZI's tile pyramid covers all zoom levels.

The viewer's initial state should match sources first entry (Fresco opens with its own src; Tessera trusts the consumer to keep them in sync). When zoom crosses each threshold, Tessera asks Fresco to swap while preserving the user's viewport bounds.

Server-side helpers (unchanged from 0.1)

Tessera also ships the lazy DZI tile-generation API:

• Tessera.generate/3 — eager full-pyramid generator
• Tessera.generate_manifest/3 — just the XML manifest
• Tessera.generate_tile/4 — one tile at a time, on demand
• Tessera.Storage behaviour + Tessera.Storage.Local default

These are unchanged from 0.1 — the breaking change in 0.2 is on the client side only.