chore(deps): update rpi-rgb-led-matrix to latest upstream for Pi 5 support

Configure submodule to track upstream master branch (branch = master in
.gitmodules) so future updates are a single 'git submodule update --remote'
rather than manual SHA management.

Update first_time_install.sh to use --remote flag so fresh installs always
pull the current upstream master, not the commit recorded at clone time.

Current upstream HEAD (8907235) brings:
- PR #1886: Raspberry Pi 5 support — new RP1 PIO and RIO backends. The
  library auto-detects Pi 5 hardware at runtime; no config change required
  for basic operation. adafruit-hat-pwm is confirmed supported on Pi 5.
- PR #1833: setup.py migrated from distutils → setuptools, fixing Python
  3.12+ build failure (Pi runs Python 3.13). Previous version could not
  build the bindings at all on current Pi OS.

Expose new rp1_rio option in display_manager.py and config.template.json:
  0 (default) = PIO mode — uses Pi 5 RP1 coprocessor, minimal CPU usage
  1 = RIO mode — Registered IO, faster throughput, higher CPU; note that
      gpio_slowdown has inverted effect in this mode

No API changes to RGBMatrix, RGBMatrixOptions, or FrameCanvas. Pi 4 and
earlier hardware is unaffected — rp1_rio is silently ignored on non-Pi-5.

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

config/config.template.json

@@ -112,7 +112,8 @@
             "limit_refresh_rate_hz": 100
         },
         "runtime": {
-            "gpio_slowdown": 3
+            "gpio_slowdown": 3,
+            "rp1_rio": 0
         },
         "display_durations": {},
         "use_short_date_format": true,