Improve History's seek startup time and recordings query performance (#24011)

* serve a segment startup ladder so seeks begin playing sooner

nginx-vod was handed one 10s segment per recording file, so every playlist start had to download and decode a full segment before the first frame. Declare real keyframe data per clip and let nginx cut short leading segments from it.

- add vod_bootstrap_segment_durations 1000/2000/4000 so each playlist starts with 1s/2s/4s segments before settling at 10s
- emit real clip-relative keyFrameDurations (plus firstKeyFrameOffset when nonzero) from the recording keyframe index; rows without an index keep the whole-clip declaration, the only safe cut without keyframe knowledge
- drop the manifest's segment_duration field, which was always inert: nginx-vod parses only camelCase segmentDuration
- rebuild the player source at the seek target, quantized to a 10s grid, so the ladder applies to every seek and seek URLs stay repeatable for nginx's mapping and response caches
- route the seek model, in-range checks, and the stale-report guard through the source window rather than the chunk range
- bridge repositioning seeks (>2s from the last played timestamp) through the preview player and hold the release anchor one commit, so neither path paints a stale frame
- clear a pending loading timer before replacing it; an orphaned timer escaped onPlaying's clearTimeout and flashed loading mid-playback

* keep recordings queries on their indexes

Several recordings queries degraded into full scans or large sorts on big databases: the planner ignored index order, or the query shape gave it nothing tight to seek on. Reshape them into bounded seeks and add the composite index the per-stream lookups need.

- index recordings on (camera, stream_type, start_time DESC) and drop the (camera, stream_type) index it supersedes
- walk the recordings summary day by day with EXISTS probes and per-camera MIN/MAX seeks, skipping ahead over empty gaps instead of bucketing every row for the requested cameras
- run the summary endpoint on the event loop rather than the threadpool
- bound the unavailable-recordings query by start_time per camera and merge the results in Python
- bound the expire query's start_time so it seeks the retention window instead of scanning a camera's whole history
- enumerate deleted cameras with one index seek each rather than a camera NOT IN (...) scan
- compute bandwidth with segment_size filtered in a CASE projection; as a WHERE predicate it baited the planner into the (camera, segment_size) index plus a full sort of the camera's history
- fall back to a 1000-segment window when the recent 100 are all zero-size, so an ingest glitch doesn't report zero bandwidth
- limit the needs_refresh count instead of counting every segment
- cover sub-only and sparse calendar days, midnight-spanning day attribution, multi-camera gap merging, deleted-camera expiry, and zero-size segment runs

* fix mypy

frigate/api/media.py

@@ -598,7 +598,15 @@ def _build_vod_clip(
     clip: dict[str, Any] = {"type": "source", "path": row.path}
     if plan.clip_from_ms is not None:
         clip["clipFrom"] = plan.clip_from_ms
-    clip["keyFrameDurations"] = [plan.duration_ms]
+    if plan.key_frame_durations is not None:
+        # real gaps enable keyframe-aligned sub-file segments (bootstrap
+        # ladder); the whole-clip fallback keeps one segment per file,
+        # the only safe cut without an index
+        if plan.first_key_frame_offset_ms > 0:
+            clip["firstKeyFrameOffset"] = plan.first_key_frame_offset_ms
+        clip["keyFrameDurations"] = plan.key_frame_durations
+    else:
+        clip["keyFrameDurations"] = [plan.duration_ms]
     logger.debug(
         "VOD: added clip %s duration_ms=%s clipFrom=%s",
         row.path,
@@ -740,14 +748,15 @@ async def _vod_response(
             NGINX_VOD_MAX_CLIPS,
         )
 
+    # segmentation comes from the vod_* nginx directives plus per-clip
+    # keyFrameDurations; a segment_duration field here was always ignored
+    # (nginx-vod parses only camelCase segmentDuration)
     hour_ago = datetime.now() - timedelta(hours=1)
     content = {
         "cache": hour_ago.timestamp() > start_ts,
         "discontinuity": force_discontinuity or use_discontinuity,
         "consistentSequenceMediaInfo": True,
         "durations": durations,
-        # aligns segments to recording file boundaries
-        "segment_duration": max(durations),
         "sequences": [{"clips": clips}],
     }
     if use_discontinuity: