fix: add opencode caveman-compress command

[4jokxon]

Problem

The opencode installer test suite expects src/plugins/opencode/commands/caveman-compress.md to exist, but the file was missing. This caused test #13 to fail:

not ok 13 - opencode fresh install drops plugin, commands, agents, skills, AGENTS.md, opencode.json
error: 'command caveman-compress.md missing'

Fix

Added the missing caveman-compress.md command file that loads the caveman-compress skill and rewrites context/memory files to terse caveman style.

Test

npm test
tests 51
pass 51
fail 0

All 51 tests now pass (was 47 pass, 4 fail before this fix).

[epulla]

I just got this issue:

opencode install failed: ENOENT: no such file or directory, copyfile '~/Lib
rary/Caches/pnpm/dlx/31d2664d2a961ecbf25e00f3993ca7f8a0e8944e9d94b754bc6a47c682993af4/19e
3c12e7c6-118f5/node_modules/.pnpm/caveman-installer@https+++codeload.github.com+JuliusBru
ssee+caveman+tar.gz+18e45320a0b1_a60bfef170c4248c40e92217c94fc7b3/node_modules/caveman-in
staller/src/plugins/opencode/commands/caveman-compress.md' -> ~/.config/open
code/commands/caveman-compress.md'

had to manually add the caveman-compress.md file to ~/.config/opencode/commands/