Make gRPC a default dependency, remove .zenflow from repo

Move grpcio and protobuf from the [grpc] optional extra into base
dependencies — the package is not useful without gRPC support.
Remove the [grpc] extra entirely and update all install instructions,
Dockerfiles, and docs to use plain `pip install qr-sampler`.

Also untrack .zenflow/ (development task tracking) and .claude/
by adding them to .gitignore.

Author: alchemystack

.gitignore

@@ -44,5 +44,11 @@ node_modules/
 # Environment files
 .env
 
+# Claude Code
+.claude/
+
+# Zenflow (development task tracking)
+.zenflow/
+
 # Setuptools SCM
 src/qr_sampler/_version.py