go2rtc and several IP cameras still emit a warm-up / black frame on every
fresh MJPEG connection — even with the v0.2.4b2 warm-up-skip fix it
slipped through intermittently for @nkm8's setup. His own bisect named
the clean solution: go2rtc exposes /api/frame.jpeg as a dedicated
single-frame endpoint that never returns the encoder's stale keyframe.
Adds an optional external_camera_snapshot_url column on printers. When
set, every single-frame capture path (snapshot endpoint, [SNAPSHOT]
notification thumbnails, [PHOTO-BG] finish photo, layer timelapse,
Obico ML, plate-detect / calibrate-plate) routes through _capture_snapshot
on the override URL via plain HTTP GET, bypassing the warm-up dance.
Live view stays on the configured stream URL — only single-frame
captures use the override. Override is camera-type-agnostic. SSRF guard
applies (existing _sanitize_camera_url allowlist). Empty string treated
as unset.
Settings UI: new "Snapshot URL (optional)" input + Test button under
External Cameras, hidden for camera_type=snapshot since the live URL is
already a single-frame source. en + de fully translated; 6 other locales
seeded with English copy.
5 backend tests pin the routing contract; 3 frontend tests pin the
input + debounced PATCH. Documented in
bambuddy-wiki/docs/features/camera.md with the go2rtc example.