P4.3: render seeded board with real gem sprites (sx, iOS sim)

Adopt the modules/ui UIPipeline framework (as the chess reference app does)
and replace the P0 placeholder quad with a BoardView (View protocol, modeled
on chess/board_view.sx):
- background.png fills the screen; an 8x8 cell.png grid is centered in the
  safe area; each cell's gem is sampled from gems.png by UV column = gem index
  (0=red .. 5=purple).
- Drive it from board.sx seeded with 1337 (the board_init golden's seed), so
  the on-screen layout matches that snapshot gem-for-gem.

main.sx now hosts the view via UIPipeline (Metal on iOS, GL on desktop) and
heap-allocates the board/asset state behind pointers (UFCS method calls on a
value-typed global mutate a copy, so mutable state must live behind a pointer
as the reference app does).

Vendor the C deps the UI module's image/font path needs (stb_image,
stb_truetype, kb_text_shape, file_utils); their #include "vendors/..." paths
resolve relative to the project root.

Evidence: ios-sim build links clean; tools/run_tests.sh 11/11 pass; running
app captured at goldens/p4_board.png.

vendors/file_utils/file_utils.c

@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef __ANDROID__
+#include <android/asset_manager.h>
+
+// Caller-installed AAssetManager pointer. Chess's android_main extracts
+// it from `app->activity->assetManager` (via sx-side platform module's
+// `g_android_asset_manager` global) and feeds it here once at startup.
+// Until the setter has been called, Android falls through to fopen —
+// gives a predictable "file not found" rather than a NULL-deref.
+static AAssetManager* g_aam = NULL;
+
+void sx_android_set_asset_manager(void* m) {
+    g_aam = (AAssetManager*)m;
+}
+#endif
+
+unsigned char* read_file_bytes(const char* path, int* out_size) {
+#ifdef __ANDROID__
+    if (g_aam != NULL) {
+        // AAssetManager paths are relative to the APK's `assets/`
+        // directory. Strip a leading "assets/" so callers can use the
+        // same paths across iOS/macOS/Android (those platforms read
+        // assets via `assets/...` rooted in the bundle or CWD).
+        const char* lookup = path;
+        if (strncmp(path, "assets/", 7) == 0) {
+            lookup = path + 7;
+        }
+        AAsset* a = AAssetManager_open(g_aam, lookup, AASSET_MODE_BUFFER);
+        if (a != NULL) {
+            off_t n = AAsset_getLength(a);
+            *out_size = (int)n;
+            unsigned char* buf = (unsigned char*)malloc((size_t)n);
+            if (buf != NULL) {
+                memcpy(buf, AAsset_getBuffer(a), (size_t)n);
+            }
+            AAsset_close(a);
+            return buf;
+        }
+        // Falls through to fopen — useful when assets land in the data
+        // dir via extraction or app updates.
+    }
+#endif
+    FILE* f = fopen(path, "rb");
+    if (!f) return 0;
+    fseek(f, 0, SEEK_END);
+    *out_size = (int)ftell(f);
+    fseek(f, 0, SEEK_SET);
+    unsigned char* buf = (unsigned char*)malloc(*out_size);
+    fread(buf, 1, *out_size, f);
+    fclose(f);
+    return buf;
+}

vendors/file_utils/file_utils.h

@@ -0,0 +1,13 @@
+#ifndef FILE_UTILS_H
+#define FILE_UTILS_H
+
+unsigned char* read_file_bytes(const char* path, int* out_size);
+
+#ifdef __ANDROID__
+// Install the AAssetManager that `read_file_bytes` consults for paths
+// rooted inside the APK. Caller is responsible for passing the manager
+// from `ANativeActivity->assetManager` before any read_file_bytes call.
+void sx_android_set_asset_manager(void* m);
+#endif
+
+#endif

vendors/kb_text_shape/kb/LICENSE

@@ -0,0 +1,19 @@
+zlib License
+
+(C) Copyright 2024-2025 Jimmy Lefevre
+
+This software is provided 'as-is', without any express or implied
+warranty.  In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not
+  claim that you wrote the original software. If you use this software
+  in a product, an acknowledgment in the product documentation would be
+  appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be
+  misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.

vendors/kb_text_shape/kb_text_shape_impl.c

@@ -0,0 +1,2 @@
+#define KB_TEXT_SHAPE_IMPLEMENTATION
+#include "kb/kb_text_shape.h"

vendors/kb_text_shape/kbts_api.h

@@ -0,0 +1,15 @@
+// Minimal API declarations for SX import.
+// Only the functions/types we actually use — avoids parsing the full 30k-line header.
+
+typedef struct kbts_shape_context kbts_shape_context;
+typedef struct kbts_font kbts_font;
+
+kbts_shape_context *kbts_CreateShapeContext(void *Allocator, void *AllocatorData);
+void kbts_DestroyShapeContext(kbts_shape_context *Context);
+kbts_font *kbts_ShapePushFontFromMemory(kbts_shape_context *Context, void *Memory, int Size, int FontIndex);
+void kbts_GetFontInfo2(kbts_font *Font, void *Info);
+void kbts_ShapeBegin(kbts_shape_context *Context, unsigned int ParagraphDirection, unsigned int Language);
+void kbts_ShapeUtf8(kbts_shape_context *Context, const char *Utf8, int Length, unsigned int UserIdGenerationMode);
+void kbts_ShapeEnd(kbts_shape_context *Context);
+int kbts_ShapeRun(kbts_shape_context *Context, void *Run);
+int kbts_GlyphIteratorNext(void *It, void **Glyph);

vendors/stb_image/stb_image_impl.c

@@ -0,0 +1,2 @@
+#define STB_IMAGE_IMPLEMENTATION
+#include "stb_image.h"

vendors/stb_image/stb_image_write_impl.c

@@ -0,0 +1,2 @@
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "stb_image_write.h"

vendors/stb_truetype/stb_truetype_impl.c

@@ -0,0 +1,2 @@
+#define STB_TRUETYPE_IMPLEMENTATION
+#include "stb_truetype.h"