feat: apply per-version patches during kernel build

Add a `patches/<kernel-version>/` mechanism: any .patch files placed in
that directory are applied with `git apply` after the source tree is
reset to the kernel tag and the .config is copied into place, before
`make olddefconfig`. Versions without a patch directory are built
unmodified, so this commit is a no-op until patches are added.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Nikita Kalyazin <nikita.kalyazin@e2b.dev>

Author: kalyazin

build.sh

@@ -59,6 +59,17 @@ function build_version {
   # Configs live in configs/{arch}/
   cp ../configs/"${TARGET_ARCH}/${version}.config" .config
 
+  # Apply per-version patches if any exist under patches/<version>/
+  local patch_dir="../patches/${version}"
+  if [ -d "$patch_dir" ]; then
+    echo "Applying patches from $patch_dir"
+    for p in "$patch_dir"/*.patch; do
+      [ -e "$p" ] || continue
+      echo "  -> $(basename "$p")"
+      git apply --verbose "$p"
+    done
+  fi
+
   # Set up cross-compilation if building arm64 on x86_64
   local make_opts=""
   if [[ "$TARGET_ARCH" == "arm64" ]]; then