Share AMOLED brightness control and optional Brookesia integration

[Y1hsiaochunnn]

The three AMOLED board definitions referenced duplicated Brookesia brightness plugins. Move the hardware brightness command into a public helper and share one explicit optional plugin, preserving the board features and runtime brightness controls.

• Keep display/touch, audio, SD, PMU, peripheral, and hardware-default source in boards/<model>/. Remove automatic Brookesia dependencies from board YAML.
• Expose waveshare_amoled_set_brightness() in include/waveshare_amoled.h so ordinary Board Manager applications can control the supported QSPI AMOLED panels without Brookesia.
• Share the optional adapter under integrations/brookesia_hal_custom/. Preserve its brightness setter/getter, 0–100 percent range, mutex, cached value, plugin/interface names, display group, and defaults. Keep all three original application profiles under profiles/<model>/.
• Depend directly on the HAL interface, using the same display_lcd group from Board Manager instead of including the full HAL adaptor for that constant. Document opt-in setup and upstream constraints: Brookesia 0.8 lib_utils requires IDF 6.0–6.2; the standalone adapter does not depend on HAL adaptor 0.8.4's separate Board Manager 0.5.* constraint.

Validation for 93028a8: 22 helper/host tests, metadata/catalog/navigation checks, actionlint, package contents, and Markdown audit passed (one expected range-audit notice for the preserved upstream changelog). Host C tests check brightness command encoding, scaling, clamping, invalid handles, and IO-error propagation. Hardware source and the three application profiles remain byte-identical to the base. All eleven local builds passed: eight plain builds across IDF v5.5.5/v6.1 plus three optional adapter builds on its native IDF v6.1, Board Manager 0.7.2. All eleven Actions builds passed on the same commit, along with metadata and aggregate checks. A separate IDF 6.1 consumer fetched this exact commit through Component Manager, discovered the 1.8 board under managed_components/waveshare__waveshare_boards, and compiled both the public brightness call and the optional adapter successfully. Adapter builds also check that the plugin and brightness getter/setter are linked and no HAL adaptor dependency is resolved. Physical board behavior and an unmodified full Brookesia application are not validated.