Add AI-upscaled critter/object art as a new MDL mod type

Extends the MDL system beyond text overrides: bitmaps/<label>.json
names a model/scale and resource list, and mdlp extracts each
resource's frames, runs them through an ONNX Runtime CPU upscaler
baked into mdlp-image, re-quantizes to the game's palette, and writes
the result back - same build-time pipeline as message overrides.

Adds animgallery, a standalone viewer that renders any data
directory's animated resources as an HTML/GIF gallery with a
checkbox-driven MDL JSON generator, and -only-changed to preview just
what a mod overrides against the base game.

Fixes a real data race in hacked's ChangeNotifier.hashAll() (found via
go build -race causing non-deterministic resource counts), via a new
numbered patch rather than editing the vendored source.

Adds engine-patches/, a general-fixes counterpart to
android/engine-patches/ now staged and applied to the desktop builds
too (previously unpatched): a real GL_UNPACK_ROW_LENGTH stride bug, an
audio error-logging improvement, and two critter-rendering fixes -
mod art was losing to the base game's own re-opened resource files,
and critters rendered at the wrong size/position once that was fixed,
both from how the billboard renderer derives on-screen size and
placement straight from bitmap pixel dimensions.

Updates README.md and AGENTS.md to document engine-patches/.

modding/README.md

@@ -23,13 +23,13 @@ repository.
     of `hacked/` at build time (same pattern as the root project's
     `android/engine-patches/`, see the repository root's
     [AGENTS.md](../AGENTS.md) section 6) - `hacked/` itself is never edited
-    in place.
+    in place. See section 1.1 for what each patch does.
   - `sqweek-dialog/` - `github.com/sqweek/dialog`, `hacked`'s native
     file-dialog dependency. Vendored at the exact version `hacked/go.mod`
     would otherwise pull from the module proxy (ISC License), so it can be
-    patched the same way as `hacked/` itself (see section 2's crash fix).
+    patched the same way as `hacked/` itself (see section 1.1).
   - `sqweek-dialog-patches/` - patches for `sqweek-dialog/`, same pattern as
-    `hacked-patches/`.
+    `hacked-patches/` (section 1.1).
   - `mdlp/` - the **Mod Definition Language Processor** (section 4). First-party
     Go source, not vendored - edit it directly, no patch system needed.
   - `ss-specs/` - [InkyBlackness ss-specs](https://github.com/inkyblackness/ss-specs),
@@ -63,6 +63,40 @@ support (level/resource files, `res/data/`); this folder is about the
 external tools that create and inspect that content, not about changing the
 engine itself.
 
+### 1.1. Patch reference
+
+`src/hacked-patches/` and `src/sqweek-dialog-patches/` (applied to scratch
+copies of `src/hacked/` and `src/sqweek-dialog/` respectively) are both
+plain, numbered patch files applied in order at build time - neither
+vendored source is ever modified in place. What each one does:
+
+`src/hacked-patches/`:
+
+- **`01-use-patched-dialog.patch`** - adds a `go.mod` `replace` directive
+  pointing `github.com/sqweek/dialog` at the local, patched
+  `../sqweek-dialog` instead of the upstream module, so `hacked` (and
+  anything else building against this source, such as `mdlp`/`animgallery`)
+  picks up the crash fix below.
+- **`02-fix-hashall-race.patch`** - fixes a real data race in
+  `ss1/resource/ChangeNotifier.go`'s `hashAll()`: it hashes many resources
+  concurrently (one goroutine per ID) to detect what changed after a
+  modification, but only guarded the resource *lookup* with a mutex, not
+  the actual block-reading inside `hashResource()` - resources from the
+  same underlying file share a stateful reader, so concurrent unguarded
+  reads corrupted each other, non-deterministically. Found via `go build
+  -race` after `animgallery` produced a different resource count on every
+  run against the exact same input. The mutex now guards the whole hash
+  computation per resource, not just the lookup.
+
+`src/sqweek-dialog-patches/`:
+
+- **`01-xinitthreads.patch`** - adds `XInitThreads()` before `gtk_init()`
+  in the Linux backend. Without it, `hacked` segfaults the moment a native
+  GTK3 dialog (file/folder browse) opens while a GLFW/OpenGL context is
+  live: GLFW's own X11 backend installs a process-wide Xlib error handler
+  that conflicts with GTK's unless Xlib has been told up front that it
+  will be used from multiple threads.
+
 ## 2. Building `hacked`
 
 Packages `dist/<version>.linux64.tgz` and `dist/<version>.win64.zip` (native
@@ -139,11 +173,16 @@ Rebecca Lansing's first email.
 
 ## 4. Mod Definition Language (mods/)
 
-The workflow above is manual and its result (whatever you clicked through in
-`hacked`) isn't checked into git. `mods/` holds the same kind of edits as
-plain, reviewable JSON instead, and `mdlp` (the **Mod Definition Language
-Processor**, `mdlp/`) turns them into the same kind of mod folder and a zip,
-reproducibly and offline.
+MDL is a small, declarative JSON format for describing a mod's content -
+one file per piece of content (a message override, an upscaled sprite, and
+so on), naming the game resource it touches and the values to set, rather
+than the resource's actual binary data. `mdlp` (the **Mod Definition
+Language Processor**, `mdlp/`) reads these files and produces the same kind
+of mod folder `hacked` itself would save, reproducibly and offline. Since a
+plain-text description is all that's checked into git, mods stay reviewable
+and reproducible from the game's own data alone (see section 4.3) - unlike
+the workflow in section 3, whose result only ever lives in whatever you
+clicked through in `hacked`.
 
 ### 4.1. Layout
 
@@ -208,8 +247,12 @@ Needs the game's own data directory at `../res/assets/ss_ee/data` (see the
 root [README.md](../README.md) section 3) as read-only reference data, so
 overrides that touch only some fields of a message can inherit the rest.
 
-Output lands in `dist/mods/<mod-name>/`: a `mod/` folder (the same shape
-`hacked`'s own Project window Save produces) and `<mod-name>.zip`.
+Output lands in `dist/mods/<mod-name>/mod/` (the same shape `hacked`'s own
+Project window Save produces) for each mod, plus one combined
+`dist/questshock-mods.zip` packaging all of them together. Nothing but
+`mods/`'s own JSON/text files needs to be checked into git - the game's own
+data (already required locally, already git-ignored) plus those files is
+always enough to reproduce this output from scratch.
 
 Test every built mod at once with `run-mods.sh` (Linux) / `run-mods.bat`
 (Windows), copied into the root project's own `dist/`/`dist-win/` by