fix(v1.2.3): false-positive "Remove core Downloader" notification

[Copilot]

hass.config.components can contain "downloader" at boot even when downloader: is absent from configuration.yaml, causing the conflict notification to fire on every restart for users who never configured the built-in integration.

Changes

• Reliable detection — replaces "downloader" in hass.config.components with "downloader" in hass.services.async_services(). Services are only registered after a successful async_setup(), making this a true signal that downloader: is explicitly configured.
• Deferred execution — wraps the check in hass.async_at_start() so it runs after HA has fully started and all YAML integrations have registered their services. Also handles the late-install case (HA already running) automatically.
• Version bump — manifest.json → 1.2.3; CHANGELOG.md updated.

# Before — unreliable, fires even without downloader: in configuration.yaml
if "downloader" in hass.config.components:
    ...

# After — deferred, service-based check
@callback
def _check_downloader_conflict(_: HomeAssistant) -> None:
    if "downloader" in hass.services.async_services():
        ...

hass.async_at_start(_check_downloader_conflict)

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