fix(pi5): auto-detect Pi 5 and force rgbmatrix rebuild when rp1_rio missing (#341)

* fix(pi5): auto-detect Pi 5 and force rgbmatrix rebuild when rp1_rio missing

first_time_install.sh:
- Detect Pi 5 from /proc/device-tree/model at startup
- Step 6 skip logic now also checks hasattr(RGBMatrixOptions(), 'rp1_rio'):
  if the installed library lacks rp1_rio (built before Pi 5 support was added)
  the build is forced even when the module is already importable. This is the
  root cause of mmap errors to 0x3f000000 (Pi 3 bus) on Pi 5 hardware.
- After a successful Pi 5 build, verify rp1_rio is present and print a
  diagnostic with the submodule update command if it's still missing.

src/display_manager.py:
- rp1_rio warning now names the symptom (mmap to 0x3f000000) and gives the
  exact fix command so users can act immediately from the log.

README.md:
- Remove "Pi 5 is unsupported" — Pi 5 is fully supported since the library
  submodule includes rp1_pio and rp1_rio backends.
- Document the forced-rebuild command for users migrating from Pi 4.
- Fix gpio_slowdown guidance: Pi 5 PIO mode uses 1–2, not 5.

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

* fix(install): only append Pi 5 suffix in skip-build message when IS_PI5=1

${IS_PI5:+...} expands whenever IS_PI5 is set, including when it's "0".
Replace with an explicit equality check so the suffix only appears on
actual Pi 5 installs.

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

---------

Co-authored-by: Chuck <chuck@example.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/display_manager.py

@@ -110,9 +110,10 @@ class DisplayManager:
                     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"
+                        "rp1_rio is set in config but the installed rgbmatrix library does "
+                        "not support it — the library was likely built without Pi 5 RP1 "
+                        "support (mmap to 0x3f000000 instead of RP1 chip). "
+                        "Fix: sudo RPI_RGB_FORCE_REBUILD=1 ./first_time_install.sh"
                     )
             
             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}")