fitness: add ExerciseDB v2 scrape data, media, and ID mapping

Scrape scripts for ExerciseDB v2 API (scrape-exercises.ts,
download-exercise-media.ts), raw data for 200 exercises with
images/videos, and a 1:1 mapping from ExerciseDB IDs to internal
kebab-case slugs (exercisedb-map.ts). 23 exercises matched to
existing internal IDs, 177 new slugs generated.

.env.example

@@ -32,3 +32,6 @@ OLLAMA_URL="http://localhost:11434"  # Local Ollama server URL
 
 # HuggingFace Transformers Model Cache (for nutrition embedding models)
 TRANSFORMERS_CACHE="/var/cache/transformers"  # Must be writable by build and runtime user
+
+# ExerciseDB v2 API (RapidAPI) - for scraping exercise data
+RAPIDAPI_KEY="your-rapidapi-key"