docs: Add README for daplink_bridge driver.

[nedseb]

Description

The new daplink_bridge module (created in #256) has no README. It needs documentation covering:

• I2C address and device identification
• Status/error registers and busy polling
• Config zone API (read, write, clear)
• Architecture diagram showing relationship with daplink_flash and steami_config

Tasks

• Create lib/daplink_bridge/README.md
• Document all public API methods
• Add basic usage example
• Add architecture diagram

[nedseb]

Le README existe déjà sur main — il a été ajouté dans le cadre du refactoring #256 (PR #285).