feat: adaptive keyframe count based on video duration

- Replace fixed 5-8 keyframe limit with duration-based adaptive sizing
- Candidate frames: clamp(duration_min × 2, 30, 120)
- Keyframe cap: clamp(duration / 150s, 8, 30)
- 30min video → 12 keyframes (was 8), 60min → 24, 120min → 30
- Short videos (<12min) still get floor of 8 keyframes
- Add Ollama keep-alive config doc to PROGRESS.md (OLLAMA_KEEP_ALIVE=-1)
- Update config.yaml and config.yaml.example with new video params

fam-core/config/config.yaml

@@ -18,7 +18,9 @@ database:
 
 scheduler:
   scan_interval: 60
-  video_dir: "/volume1/surveillance"
+  # E2E 测试期间指向独立测试目录（正式目录 /volume1/surveillance 有 285 个历史视频，
+  # 全量建任务会导致 100GB 跨公网上传，待与用户确认回补策略后再切回）
+  video_dir: "/volume1/web/sentinel-home-ai/e2e-test"
   video_extensions: [".mp4", ".mkv", ".avi"]
   file_stable_seconds: 60
   camera_name: "客厅"