Stage 1: project setup, Exercise Library, both Mode designs and the Mode switch

- Flutter Android app on CookIT's stack (provider, shared_preferences, gen-l10n)
- tools/exercise-import turns free-exercise-db into 876 bundled Exercises
  with 1,746 WebP images (20 MB); stretching -> Stretching, rest -> Workout
- ZenStyle tokens per Mode: calm rounded sage/teal with breath ripples vs.
  dark ember-to-red with floor-tape slashes; the theme morphs at each
  Mode's own pace
- Remembered global Mode switch, Plans / Library / History tabs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/exercise-import/convert.py

@@ -0,0 +1,25 @@
+"""Usage: python convert.py <free-exercise-db checkout> [output folder]
+
+The output folder defaults to the app's assets/exercises.
+"""
+
+import collections
+import sys
+from pathlib import Path
+
+from exercise_import import run
+
+
+def main() -> None:
+    if len(sys.argv) < 2:
+        sys.exit(__doc__)
+    source = Path(sys.argv[1])
+    output = Path(sys.argv[2]) if len(sys.argv) > 2 else Path(__file__).resolve().parents[2] / "assets" / "exercises"
+    exercises = run(source, output)
+    modes = collections.Counter(e["mode"] for e in exercises)
+    size = sum(f.stat().st_size for f in (output / "images").glob("*.webp"))
+    print(f"{len(exercises)} Exercises ({dict(modes)}), images {size / 1_000_000:.1f} MB -> {output}")
+
+
+if __name__ == "__main__":
+    main()