Record where a linear DNG too large for one texture goes

ARCH §5.3 still described only a tile cache nobody built; it now says
what 0.19.0 tiles and what it does not: a linear DNG past PROXY_EDGE
opens on a reduced copy, a finer render samples a full-resolution
window, and the export is cut into halo-grown tiles. display-and-
extension.md's FR-DSP-2 row said absent, outstanding.md said the halo
had nothing to read it and that such a file fell to the embedded
preview.

rawler now builds from third_party, which ARCH's stack table and §3.2,
the root Cargo.toml's comment ("two upstream crates ... for Android")
and third_party/README.md's bump procedure did not know; the README
also names each vendored crate's licence. panorama.md and the manual
say a composite this wide develops and exports.

third_party/README.md

@@ -11,17 +11,24 @@ The first commit that adds a directory is the pristine copy (from
 crate's own `Cargo.lock`). Every later commit touching it is ours, so
 `git log -p -- third_party/<dir>` is the patch and nothing else.
 
+Each directory keeps the crate's own licence files, and the crate keeps
+its licence: wgpu-hal is MIT or Apache-2.0, i-slint-renderer-skia is
+Slint's GPL-3.0-only or royalty-free or commercial choice, and rawler is
+LGPL-2.1.
+
 ## Carrying a patch forward
 
-When Slint or wgpu is bumped, the version here stops matching and cargo
-warns that the patch is unused — the build then silently goes back to the
-unpatched crate. So a bump is:
+When Slint, wgpu or rawler is bumped, the version here stops matching and
+cargo warns that the patch is unused — the build then silently goes back
+to the unpatched crate. So a bump is:
 
 1. Copy the new version in beside the old one, as its own commit.
 2. Re-apply the diff from `git log -p` on the old directory.
 3. Point `[patch.crates-io]` at the new directory and delete the old one.
-4. Re-check on the device (below) — both patches are behaviour that only a
-   rotated Android display exercises.
+4. Re-check what the patch was for. The wgpu-hal and Skia patches are
+   behaviour that only a rotated Android display exercises (below); the
+   rawler one is a linear DNG wider than 16 700 pixels, such as a
+   panorama the merge writes.
 
 Drop a patch entirely once upstream has the fix; each section says what
 upstream change would make it unnecessary.