feat: Korean language-aware compression

[gruming]

Summary

Caveman's compression rules are English-specific (drop articles, English short synonyms), so when it responds in Korean the output breaks — garbled fragments, forced/awkward translation of technical terms, unnatural phrasing. This PR makes caveman respond in the user's language and compress it natively.

When responding in Korean it now:

• uses 음슴체/개조식 (Korean's natural terse register) instead of broken grunt
• drops particles (은/는/이/가/을/를) only when grammatical role stays clear
• keeps technical terms in English — first mention 한글(English), single form after; ultra drops the gloss
• never translates/transliterates code, function/API names, or error strings

Design

• Language is orthogonal to intensity. lite/full/ultra are unchanged; the new rules just describe how each intensity manifests in Korean. No new mode names (no korean-*).
• Auto-detected, not a toggle. Caveman follows the user's input language, so it "just works" after install. wenyan-* stays an explicit Classical Chinese override and wins over the auto-detected language (wenyan = chosen style; Korean = following the user's actual language).
• English behavior is unchanged — every hunk is additive; existing English rules/examples are untouched. Backward compatible.

Changes

• skills/caveman/SKILL.md — new ## Language + ## Korean sections, Korean lite/full/ultra examples, description note. (Single source of truth; the plugins/ mirror + dist/ are left for CI sync per CONTRIBUTING.)
• src/rules/caveman-activate.md — language-aware line for the always-on rule body.
• README.md — short Korean section + What You Get row.

Test plan

Ran the edited SKILL.md as a system prompt through claude -p (mirrors the eval harness setup):

• Korean concept question -> natural 음슴체, English technical terms preserved
• Destructive op (DROP COLUMN) -> auto-clarity drops to plain prose for the warning, SQL preserved
• ultra -> max compression, English terms only, no 병기 gloss
• English prompt -> unchanged English caveman, no Korean leakage