tests: Add board qualification tests for buzzer.

[nedseb]

Description

Add board qualification tests for the audio buzzer (SMT-0825-S-HT-R) on the STeaMi board.

Component

Component	Pin name	STM32WB55 Pin	Interface
Buzzer	SPEAKER	PA11	PWM

Scenario: tests/scenarios/board_buzzer.yaml

Tests

1. Buzzer tone 440Hz — generate a 440Hz tone for 500ms via PWM
2. 440Hz audible — manual confirmation ("Avez-vous entendu un bip ?")
3. Frequency sweep — sweep from 200Hz to 2000Hz in 100Hz steps
4. Sweep audible — manual confirmation ("Avez-vous entendu un balayage ?")

All tests use hardware_script + manual actions (hardware mode only).

Depends on

• tests: Extend test framework for driverless board qualification scenarios. #83 (framework extension for `type: board` scenarios)