Adds GET /api/v1/stats/summary, gated by HOMEPAGE_API_KEY env var and
X-API-Key header (hmac.compare_digest, matches the liveview pattern).
Payload:
nodes / online / offline / unknown
pending_devices (status='pending')
zigbee_devices (Node.ieee_address IS NOT NULL)
last_scan_at (max ScanRun.finished_at)
Disabled by default — endpoint returns 403 unless HOMEPAGE_API_KEY is set.
README documents activation and ships a ready-to-paste gethomepage
`customapi` widget snippet.
Tests cover: disabled-by-default, missing header, wrong key, empty DB,
and full aggregation across nodes/pending/zigbee/scan-runs.
Pouzor