Rename pkg/predict to pkg/run and update CLI references
Rename the Go prediction package from pkg/predict/ to pkg/run/:
- predictor.go → runner.go: Predictor → Runner, NewPredictor → NewRunner,
Predict() → Run(), endpoint returns 'runs'
- api.go, input.go: package name updated to 'run'
Update CLI files that reference the package:
- train.go: predict.NewPredictor → run.NewRunner
- predict.go: already updated in Phase 1, import verified
- build.go: help text 'cog predict' → 'cog run'
- init_test.go: expect run.py instead of predict.py from cog init
