Replace hardcoded config and directory scan with YAML config and explicit clip list

- config.py constants -> config/config.yaml (user-editable, git-ignored)
- Questions and defaults now defined in the YAML, including per-question defaults
- ClipSelector no longer scans the data dir; reads a user-provided clips.txt instead
- Removed --daily / --time / --skip-existing-day args
- video_loader now samples frames evenly across the full clip
- pyyaml added as a dependency

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

src/river_annotation_tool/config.py

@@ -1,44 +1,38 @@
-class Config:
-    DISPLAY_MAX = 480
-    FPS_FALLBACK = 25
-    MAX_FRAMES = 100
+from dataclasses import dataclass, field
+from pathlib import Path
+
+import yaml
 
 
-QUESTIONS = [
-    (
-        "River",
-        [
-            ("flow", "Flow Regime", ["Turbulent", "Laminar", "Uncertain"]),
-            ("shadows", "Strong Shadows", ["Yes", "No", "Uncertain"]),
-            ("artifacts", "Artifacts on River", ["Yes", "No", "Uncertain"]),
-        ],
-    ),
-    (
-        "Scene",
-        [
-            ("lighting", "Lighting", ["Day", "Night", "Uncertain"]),
+@dataclass
+class AppConfig:
+    display_max: int = 480
+    fps_fallback: int = 25
+    max_frames: int = 100
+    data_dir: str = "data/clips"
+    out_dir: str = "data/annotation_results"
+    clips_file: str = "config/clips.txt"
+    questions: list = field(default_factory=list)
+
+    def get_questions(self):
+        return [
             (
-                "exposure",
-                "Exposure",
-                ["Overexposed", "Underexposed", "Both", "Normal", "Uncertain"],
-            ),
-        ],
-    ),
-    (
-        "Weather",
-        [
-            ("snowing", "Snowing", ["Yes", "No", "Uncertain"]),
-            ("snow_on_ground", "Snow on Ground", ["Yes", "No", "Uncertain"]),
-        ],
-    ),
-]
+                s["section"],
+                [
+                    (
+                        item["key"],
+                        item["label"],
+                        [str(o) for o in item["options"]],
+                        str(item["default"]) if item.get("default") is not None else None,
+                    )
+                    for item in s["items"]
+                ],
+            )
+            for s in self.questions
+        ]
 
-DEFAULTS = {
-    "flow": "Laminar",
-    "shadows": "No",
-    "artifacts": "No",
-    "lighting": "Day",
-    "exposure": "Normal",
-    "snowing": "No",
-    "snow_on_ground": "No",
-}
+
+def load_config(path: Path) -> AppConfig:
+    with open(path) as f:
+        data = yaml.safe_load(f)
+    return AppConfig(**data)