Migrate batch 2

[zawadzkidiana]

Summary

Migrates 10 samples from cmd/samples/recipes/ to the new self-contained structure in new_samples/.Each sample is now a standalone folder with its own main.go, worker.go, README.md, and generator.

Samples Added

Sample	Description
branch	Parallel activity execution
timer	Timeout and delay handling
greetings	Sequential activity execution
pickfirst	Race activities, use first result
choice	Conditional execution based on activity results
cancelactivity	Graceful cancellation with cleanup
delaystart	Deferred workflow execution
dynamic	Invoke activities by string name
splitmerge	Split work, process in parallel, merge results
signalcounter	Multiple signals with ContinueAsNew

Changes

• Copied workflow code from cmd/samples/recipes/
• Exported function names for registration
• Added generator files for boilerplate
• Added README with diagrams and usage instructions for each sample