Preserve ReKarel language in runner

[pabo99]

Adds rk as a first-class runner language, preserving it through compile/run as Main.rk.

Also updates the runner sandbox image to use the ReKarel-capable omegajail release and Karel runtime assets.

Tests

• Built local runner image: omegaup/runner-ci:rk-smoke
• Ran omegaup-runner -oneshot=ci with a .rk ReKarel solution
• Verified compile/run path uses rk and returns AC

Additional local smoke tests:

• rk: passed, AC
• kj: passed, AC
• py3: passed, AC
• go: passed, AC with MemoryLimit: 256 MiB

The first Go smoke with the default 32 MiB problem limit compiled successfully with omegajail v3.11.2, but failed at runtime with:

fatal error: failed to reserve page summary memory

Fixes: #148

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 41.45%. Comparing base (63d5646) to head (4b3a1ab).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #149      +/-   ##
==========================================
+ Coverage   41.29%   41.45%   +0.16%     
==========================================
  Files          25       25              
  Lines        6868     6868              
==========================================
+ Hits         2836     2847      +11     
+ Misses       3770     3759      -11     
  Partials      262      262              

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