Add linux prebuild stuff

scripts/bootstrap_sdl_linux.sh

@@ -1,12 +1,35 @@
 #!/usr/bin/env bash
+# One-time bootstrap: builds SDL3 from source and installs it into prebuilt/linux/.
+# Run this once on the Linux remote after cloning. Re-run only when upgrading SDL.
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 PROJECT_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
-SDL_SOURCE="$PROJECT_ROOT/external/SDL"
-BUILD_DIR="$PROJECT_ROOT/out/build/_sdl_build/linux"
+SDL_VERSION="${1:-3.2.10}"
+BUILD_TYPE="${2:-Release}"
+BUILD_DIR="$PROJECT_ROOT/out/build/_sdl_bootstrap/linux"
 PREBUILT_DIR="$PROJECT_ROOT/prebuilt/linux"
-BUILD_TYPE="${1:-Release}"
+SDL_SOURCE="$BUILD_DIR/SDL-src"
+
+# Install build dependencies (Debian 12 bookworm)
+echo "Checking build dependencies..."
+sudo apt-get update -qq
+sudo apt-get install -y --no-install-recommends \
+    ninja-build cmake build-essential \
+    gcc-12 g++-12 \
+    libx11-dev libxext-dev libxrandr-dev libxcursor-dev libxi-dev \
+    libwayland-dev libpulse-dev libasound2-dev \
+    libgl1-mesa-dev
+
+# Download SDL source if not already present
+if [ ! -d "$SDL_SOURCE" ]; then
+    echo ""
+    echo "=== Downloading SDL3 $SDL_VERSION ==="
+    mkdir -p "$BUILD_DIR"
+    curl -L "https://github.com/libsdl-org/SDL/archive/refs/tags/release-${SDL_VERSION}.tar.gz" \
+        | tar -xz -C "$BUILD_DIR"
+    mv "$BUILD_DIR/SDL-release-${SDL_VERSION}" "$SDL_SOURCE"
+fi
 
 build_sdl() {
     local LINK_TYPE="$1"
@@ -65,20 +88,6 @@ create_dynamic_symlinks() {
     echo "=== Done ==="
 }
 
-# Install build dependencies if needed (Debian 12 bookworm)
-echo "Checking build dependencies..."
-sudo apt-get update -qq
-sudo apt-get install -y --no-install-recommends \
-    ninja-build cmake build-essential \
-    gcc-12 g++-12 \
-    libx11-dev libxext-dev libxrandr-dev libxcursor-dev libxi-dev \
-    libwayland-dev libpulse-dev libasound2-dev \
-    libgl1-mesa-dev
-
 build_sdl "dynamic"
 build_sdl "static"
-
-# Always recreate symlinks regardless of whether the build was a no-op.
-# cmake --install does not preserve symlinks and Ninja may skip the build
-# entirely if sources are unchanged, leaving the lib directory without them.
 create_dynamic_symlinks