Complete CI coverage for the exotic languages

[kserrec]

Summary

• add runnable exact-output tests for ArkScript, FatScript, bruijn, and Language 84
• provision every toolchain from an official, pinned source
• refresh each language README with reproducible run and test instructions
• mark the exotic-language CI backfill complete in the roadmap

No language implementation source needed to change.

Toolchain integrity

• ArkScript: official 4.7.1 Linux archive, SHA-256 verified
• FatScript: official 4.5.0 image pinned by digest, run read-only with networking disabled
• bruijn: exact upstream commit built with its checksum-locked Stack LTS 22.12 snapshot; only the finished relocatable bundle is cached
• Language 84: official 0.8 source archive, SHA-256 verified, built with Clang as documented

Verification

• all four test scripts matched output captured from actual runs byte-for-byte
• ArkScript and bruijn passed again through restored CI-style tool bundles
• Language 84 passed in a clean Ubuntu 24.04 container with Clang
• the full local harness reported 12 passed, 0 failed; unrelated unavailable toolchains skipped and Java remains pending on main until PR Complete Java and Kotlin CI coverage #34 lands
• workflow YAML, Bash/POSIX shell syntax, and git diff checks passed