Rename smartrun to geniusrun throughout the codebase

Updates the Go module path, cmd/smartrund -> cmd/geniusrund, the
smartrun-dev skill, .gitignore, and every reference in docs/CLAUDE.md
to match.

backend/internal/store/db.go

@@ -1,4 +1,4 @@
-// Package store is smartrun's SQLite persistence layer: activities, laps,
+// Package store is geniusrun's SQLite persistence layer: activities, laps,
 // per-second samples, workout kind rule config, and classification history.
 package store
 
@@ -15,7 +15,7 @@ import (
 //go:embed migrations/*.sql
 var migrationsFS embed.FS
 
-// DB wraps a *sql.DB opened against a smartrun SQLite database file, with
+// DB wraps a *sql.DB opened against a geniusrun SQLite database file, with
 // migrations already applied.
 type DB struct {
 	*sql.DB