feat(games): add Snake and Tetris X11 games with menu integration

Add two standalone X11 games (not DWM plugins) for the Nokia 8110 keypad:
- src/games/snake.cpp: Nokia Snake II-style game, 240x296, built-in 5x7 font
- src/games/tetris.cpp: Tetris with next-piece preview, levels, line clears

Both float as dialog windows in dwm, use a self-contained bitmap font (no
font-file dependency), and are controlled via the numeric keypad (2/4/6/8
directions, 5 action) with arrow-key fallbacks.

- scripts/build-games.sh: Docker armv7 cross-compile (mirrors build-sxmo-x11.sh)
- overlay/rootfs/usr/share/sxmo/default_hooks/sxmo_hook_games.sh: Games menu hook
- overlay/rootfs/usr/bin/sxmo_appmenu.sh: add 'Games' entry after 'Apps' and a
  games submenu case

Binaries committed to prebuilt/games and overlay/rootfs/usr/bin per repo
convention. Deployed and verified on the live device (window maps, dwm focuses
it, keypad input reaches the game).

scripts/build-games.sh

@@ -0,0 +1,74 @@
+#!/bin/sh
+# Cross-compile Bananarchy standalone X11 games (Snake, Tetris) for armv7.
+set -eu
+
+BASE_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+ROOTFS_DIR="${ROOTFS_DIR:-$BASE_DIR/rootfs}"
+if [ -e "$ROOTFS_DIR" ]; then
+  ROOTFS_DIR="$(realpath "$ROOTFS_DIR")"
+fi
+
+exec docker run --rm --network=host \
+  -e HOST_UID="$(id -u)" \
+  -e HOST_GID="$(id -g)" \
+  -v "$BASE_DIR:/bananarchy" \
+  -v "$ROOTFS_DIR:/target-rootfs" \
+  alpine:3.24 sh -eu -c '
+  cat > /etc/apk/repositories <<EOF
+https://mirror.nura.eco/postmarketos/v26.06
+https://dl-cdn.alpinelinux.org/alpine/edge/main
+https://dl-cdn.alpinelinux.org/alpine/edge/community
+https://dl-cdn.alpinelinux.org/alpine/edge/testing
+EOF
+  cp /bananarchy/keys/* /etc/apk/keys/
+
+  echo "[1/4] Installing host cross-compilation toolchain..."
+  apk add --no-cache \
+    build-base \
+    gcc-armv7 \
+    g++-armv7 \
+    binutils-armv7 \
+    pkgconf >/dev/null
+
+  echo "[2/4] Preparing armv7 sysroot (X11)..."
+  SYSROOT="/tmp/armv7-sysroot"
+  mkdir -p "$SYSROOT/etc/apk/keys"
+  cp /etc/apk/repositories "$SYSROOT/etc/apk/repositories"
+  cp /etc/apk/keys/* "$SYSROOT/etc/apk/keys/"
+  apk --root "$SYSROOT" --initdb --arch armv7 add --no-scripts \
+    alpine-baselayout \
+    musl-dev \
+    linux-headers \
+    libx11-dev >/dev/null
+
+  export PKG_CONFIG_SYSROOT_DIR="$SYSROOT"
+  export PKG_CONFIG_LIBDIR="$SYSROOT/usr/lib/pkgconfig:$SYSROOT/usr/share/pkgconfig"
+  CC="armv7-alpine-linux-musleabihf-gcc --sysroot=$SYSROOT"
+  CXX="armv7-alpine-linux-musleabihf-g++ --sysroot=$SYSROOT"
+  STRIP="armv7-alpine-linux-musleabihf-strip"
+  OPT_CFLAGS="-O2 -march=armv7-a -mtune=cortex-a7 -mfpu=neon-vfpv4 -mfloat-abi=hard -fno-plt -fomit-frame-pointer"
+
+  mkdir -p /bananarchy/prebuilt/games/usr/bin
+
+  echo "[3/4] Compiling Snake and Tetris..."
+  $CXX $OPT_CFLAGS -std=c++17 -Wall -Wextra \
+    /bananarchy/src/games/snake.cpp $(pkgconf --libs x11) \
+    -o /bananarchy/prebuilt/games/usr/bin/snake
+  $CXX $OPT_CFLAGS -std=c++17 -Wall -Wextra \
+    /bananarchy/src/games/tetris.cpp $(pkgconf --libs x11) \
+    -o /bananarchy/prebuilt/games/usr/bin/tetris
+  $STRIP --strip-unneeded /bananarchy/prebuilt/games/usr/bin/snake /bananarchy/prebuilt/games/usr/bin/tetris
+
+  echo "[4/4] Installing into overlay and (optional) target rootfs..."
+  mkdir -p /bananarchy/overlay/rootfs/usr/bin
+  cp -a /bananarchy/prebuilt/games/usr/bin/. /bananarchy/overlay/rootfs/usr/bin/
+  if [ -d /target-rootfs/usr/bin ]; then
+    cp -a /bananarchy/prebuilt/games/usr/bin/. /target-rootfs/usr/bin/
+  fi
+
+  chown -R "$HOST_UID:$HOST_GID" \
+    /bananarchy/prebuilt/games \
+    /bananarchy/overlay/rootfs/usr/bin \
+    /bananarchy/src/games
+  ls -lh /bananarchy/prebuilt/games/usr/bin/snake /bananarchy/prebuilt/games/usr/bin/tetris
+'