Configure production KV binding for workouts worker (#38)

- add explicit WORKOUTS KV binding for the production environment
- document development vs production KV IDs in the worker config

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[Codex Task](https://chatgpt.com/codex/tasks/task_e_69237937647c8325be7f1a690e7780de)

Author: rodrigogiraoserrao

cloudflare-workers/workouts/wrangler.toml

@@ -3,8 +3,13 @@ main = "worker.js"
 compatibility_date = "2025-11-23"
 
 kv_namespaces = [
+  # Development KV binding
   { binding = "WORKOUTS", id = "workouts_kv" }
 ]
 
 [env.production]
 name = "workouts-production"
+# Ensure production deployments keep the WORKOUTS KV binding intact.
+kv_namespaces = [
+  { binding = "WORKOUTS", id = "workouts_kv" }
+]