feat(video): add video upload with remux/transcode playback

Add video as a media kind in photos: streaming upload with per-kind
limits, ffprobe metadata, poster frame reusing the image variant
pipeline, and a playback object (remux when web-compatible, else
h264/yuv420p/aac transcode). Video jobs run on a separate pool with a
long lease. Frontend gains a video viewer, grid badge/duration and
video upload.

Makefile

@@ -4,8 +4,8 @@
 VERSION ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
 
 # Seed testdata parameters (see `make testdata`). Counts: ALBUMS, PHOTOS, SEED, TIMEOUT.
-# Boolean (set to 1 to enable): TAGS, COMMENTS, LIKES, SHARE, INVITES, WAIT, DRY.
-# Extra passthrough flags: ARGS.
+# Boolean (set to 1 to enable): TAGS, COMMENTS, LIKES, SHARE, INVITES, WAIT, DRY, VIDEO.
+# VIDEO requires ffmpeg on PATH; it is skipped without it. Extra passthrough flags: ARGS.
 ALBUMS ?= 2
 PHOTOS ?= 10
 SEED ?= 0
@@ -76,6 +76,7 @@ testdata:
 		$(if $(filter 1,$(LIKES)),--likes,) \
 		$(if $(filter 1,$(SHARE)),--share-links,) \
 		$(if $(filter 1,$(INVITES)),--invites,) \
+		$(if $(filter 1,$(VIDEO)),--video,) \
 		$(if $(filter 1,$(WAIT)),--wait-variants,) \
 		$(if $(filter 1,$(DRY)),--dry-run,) \
 		$(ARGS)