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/classify/rule.go

@@ -1,4 +1,4 @@
-// Package classify is smartrun's classification rule engine: it evaluates a
+// Package classify is geniusrun's classification rule engine: it evaluates a
 // user-editable AND/OR condition tree against a run's metrics to decide
 // which "workout kind" (Easy, Tempo, Threshold, ...) it belongs to. Pure
 // logic only -- no I/O, no database, no Garmin client -- so it's fully