Move questions and optical flow to separate config files; clean up config.example.yaml

- questions: extracted from config.yaml into config/questions.yaml (committed, like optical_flow_config.yaml)
- optical_flow_config_file and questions_config_file are now required fields
- data_dir and out_dir are now required (no defaults)
- filenames: trimmed to input-only in example; output filenames stay as code defaults
- annotator: remove optional guard around optical flow config loading

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/config.example.yaml

@@ -1,66 +1,21 @@
-# For local storage, set data_dir and out_dir to file-system paths:
-storage: local   # 'local' (default) or 's3'
-data_dir: data/filtered_data
-out_dir: data/annotation_results
-# For S3 storage, set storage: s3 and use bucket/prefix paths:
-# storage: s3
-# data_dir: my-bucket/clips
-# out_dir: my-bucket/annotation_results
-# Credentials are read from env vars (copy .env.example to .env):
+storage: local   # 'local' or 's3'
+
+# Required: set these to your actual paths (local path or bucket/prefix for S3)
+data_dir:
+out_dir:
+# For S3 credentials, copy .env.example to .env and fill in:
 # S3_ACCESS_KEY, S3_SECRET_ACCESS_KEY, S3_ENDPOINT_URL
+
 clips_file: config/clips.txt
 optical_flow_config_file: config/optical_flow_config.yaml
+questions_config_file: config/questions.yaml
 
 display_max: 720
 fps_fallback: 25
 max_frames: 100
 
-questions:
-  - section: River
-    items:
-      - key: flow
-        label: Flow Regime
-        options: [Turbulent, Laminar, Uncertain]
-        default: Laminar
-      - key: shadows
-        label: Strong Shadows
-        options: [Yes, No, Uncertain]
-        default: No
-      - key: artifacts
-        label: Artifacts on River
-        options: [Yes, No, Uncertain]
-        default: No
-  - section: Scene
-    items:
-      - key: lighting
-        label: Lighting
-        options: [Day, Night, Uncertain]
-        default: Day
-      - key: exposure
-        label: Exposure
-        options: [Overexposed, Underexposed, Both, Normal, Uncertain]
-        default: Normal
-  - section: Weather
-    items:
-      - key: snowing
-        label: Snowing
-        options: [Yes, No, Uncertain]
-        default: No
-      - key: snow_on_ground
-        label: Snow on Ground
-        options: [Yes, No, Uncertain]
-        default: No
-
+# Input filenames (override if your ZIP archives differ)
 filenames:
   video_in_zip: left.mp4
   video_tmp_suffix: .mp4
   zip_extension: .zip
-  mask: mask.png
-  metadata: metadata.json
-  frame: frame.png
-  overlay: overlay.png
-  mask_vis: mask_vis.png
-  gif_original_hires: video_original_hires.gif
-  gif_original_lowres: video_original_lowres.gif
-  gif_overlay_hires: video_overlay_hires.gif
-  gif_overlay_lowres: video_overlay_lowres.gif