Merge branch 'master' into worktree-mosaic-library

Renumbers the mosaic's requirement IDs out of the way of the download work
that landed on master in parallel: it had already claimed DR-163/DR-164 and
UT-162, so the mosaic layout is now DR-172, the library favourites scope
DR-173, and its composition test UT-167.

Note for the download branch: its UT-162..UT-165 rows trace to DR-163..DR-166,
none of which are defined in requirements.md — that branch defined DR-167..171
instead. Those references are orphaned and want a look; nothing here touches
them.

src/lib/components/common/CachedImage.svelte

@@ -15,7 +15,7 @@
      * Called once the bitmap is decoded, with its intrinsic pixel size. Lets a
      * layout that sizes boxes from artwork (the mosaic) use the shape the image
      * actually has rather than the one its item type suggests.
-     * TRACES: UR-075 | DR-163
+     * TRACES: UR-075 | DR-172
      */
     onNaturalSize?: (width: number, height: number) => void;
   }

src/lib/components/library/MosaicGrid.svelte

@@ -11,7 +11,7 @@
   arrives over a few hundred milliseconds, and re-packing on each arrival would
   shuffle the grid under the viewer's cursor several times over.
 
-  TRACES: UR-075 | DR-163
+  TRACES: UR-075 | DR-172
 -->
 <script lang="ts" generics="T extends { key: string; ratio: number }">
   import type { Snippet } from "svelte";

src/lib/components/library/MosaicTile.svelte

@@ -7,7 +7,7 @@
   lines would no longer line up with its neighbours. Keeping everything inside
   the box is what lets `layoutMosaic` own the geometry completely.
 
-  TRACES: UR-075 | DR-163
+  TRACES: UR-075 | DR-172
 -->
 <script lang="ts">
   import type { Snippet } from "svelte";

src/lib/components/library/libraryMosaic.ts

@@ -9,7 +9,7 @@
 // `favoritesScope` (Rust: `SearchScope::for_collection_type`). This file only
 // decides what to *call* it and where to put it.
 //
-// TRACES: UR-075, UR-067 | DR-163, DR-164 | UT-162
+// TRACES: UR-075, UR-067 | DR-172, DR-173 | UT-167
 
 import type { Library } from "$lib/api/types";
 import {

src/lib/components/library/mosaic.ts

@@ -9,7 +9,7 @@
 //
 // Presentation only — nothing here knows what a library or a media item is.
 //
-// TRACES: UR-075 | DR-163 | UT-158, UT-159, UT-160
+// TRACES: UR-075 | DR-172 | UT-158, UT-159, UT-160
 
 /** A tile to place: an opaque key and the aspect ratio (width / height) to honour. */
 export interface MosaicInput {