Upgrade Shen kernel to 41.1

[pyrex41]

Summary

Upgrade the bundled Shen kernel from S39.2 to S41.1. This refreshes the
Shen sources and the generated Go kernel so the port starts from the 41.1
initialise/repl entry points. The test programs move from
S39/Test Programs/ to kernel/tests/.

The REPL banner now reports version: S41.1.

Testing

• go build ./... and go test ./... pass.
• The 41.1 kernel loads and runs; spot-checked against the bundled
  kernel/tests/ programs, e.g. (prime*? 1000003) → true and
  (cartesian-product [1 2 3] [4 5]) →
  [[1 4] [1 5] [2 4] [2 5] [3 4] [3 5]].

Relationship to the bytecode-VM PR

This is independent of the bytecode-VM compiler PR (#50): that PR only
touches kl/, while this one only touches the generated kernel
(cmd/shen/), the bundled sources, and the test programs — zero file
overlap, so the two can merge in either order without conflict.

I've verified the two compose: with both applied, the 41.1 kernel compiles
through the bytecode VM, loads cleanly, and the kernel/tests/ programs
above produce the same correct results.

🤖 Generated with Claude Code