Fix Home Assistant 2026.8 discovery scheduling

[dr-apple]

What changed

• schedule delayed discovery through a callback-marked Home Assistant job
• add regression coverage for all delayed retry callbacks
• bump the integration to 1.0.2

Why

Home Assistant 2026.8 executed the unmarked lambda in a worker thread. It then called hass.async_create_task outside the event loop, causing runtime errors and skipped discovery scans.

Validation

• Ruff format/check
• 9 pytest tests, including delayed callback scheduling coverage