fix: deterministic submodule install + guard rp1_rio for older rgbmatrix

first_time_install.sh: remove --remote from both git submodule update
calls so first-time installs check out the pinned commit recorded in the
repo rather than whatever upstream master happens to be at install time.
The branch = master config in .gitmodules reserves --remote for an
explicit maintainer upgrade (git submodule update --remote).

display_manager.py: guard rp1_rio assignment with hasattr() so setting
the option in config does not cause an AttributeError and silently fall
through to emulator mode when running against RGBMatrixEmulator or an
older rgbmatrix build that predates the Pi 5 property. Emit a warning
instead so the operator knows the value was ignored.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

first_time_install.sh

@@ -795,7 +795,7 @@ else
         # Try to initialize submodule if .gitmodules exists
         if [ -f "$PROJECT_ROOT_DIR/.gitmodules" ] && grep -q "rpi-rgb-led-matrix" "$PROJECT_ROOT_DIR/.gitmodules"; then
             echo "Initializing rpi-rgb-led-matrix submodule..."
-            if ! git submodule update --init --remote --recursive rpi-rgb-led-matrix-master 2>&1; then
+            if ! git submodule update --init --recursive rpi-rgb-led-matrix-master 2>&1; then
                 echo "⚠ Submodule init failed, cloning directly from GitHub..."
                 git clone https://github.com/hzeller/rpi-rgb-led-matrix.git rpi-rgb-led-matrix-master
             fi
@@ -814,7 +814,7 @@ else
             cd "$PROJECT_ROOT_DIR"
             rm -rf rpi-rgb-led-matrix-master
             if [ -f "$PROJECT_ROOT_DIR/.gitmodules" ] && grep -q "rpi-rgb-led-matrix" "$PROJECT_ROOT_DIR/.gitmodules"; then
-                git submodule update --init --remote --recursive rpi-rgb-led-matrix-master
+                git submodule update --init --recursive rpi-rgb-led-matrix-master
             else
                 git clone https://github.com/hzeller/rpi-rgb-led-matrix.git rpi-rgb-led-matrix-master
             fi

src/display_manager.py

@@ -103,7 +103,14 @@ class DisplayManager:
             # Pi 5 only: 0=PIO/RP1 coprocessor (default, less CPU),
             # 1=RIO/Registered IO (faster; gpio_slowdown effect is inverted in this mode)
             if 'rp1_rio' in runtime_config:
+                if hasattr(options, 'rp1_rio'):
                     options.rp1_rio = runtime_config.get('rp1_rio')
+                else:
+                    logger.warning(
+                        "rp1_rio is set in config but the current RGBMatrixOptions "
+                        "implementation does not support it (RGBMatrixEmulator or older "
+                        "library version) — value will be ignored"
+                    )
             
             logger.info(f"Initializing RGB Matrix with settings: rows={options.rows}, cols={options.cols}, chain_length={options.chain_length}, parallel={options.parallel}, hardware_mapping={options.hardware_mapping}")