[x] Merge .omp/APPEND_SYSTEM.md into AGENTS.md
[x] Use git submodule for toolkit/ with URL git@git.sr.ht:~iacore/mpi-translation-toolkit
    (push failed: remote may not exist or SSH key not configured; run `git push -u origin main` in toolkit/)
[x] Rename terms-search/ -> terms-database/
[x] Rename skill directories with mpi- prefix
[x] Create toolkit/ and fold scripts/, references/, terms-database/, skills/ into it
[x] Update all in-repo references
[ ] Update external Hermes config:
    ~/.hermes/config.yaml: skills.external_dirs -> $MPI_PROJECT_ROOT/toolkit/skills
[x] Test
    - toolkit/terms-database/search.py runs
    - toolkit/scripts/gen-bilingual.py runs
    - no stale references to scripts/, references/, terms-search/, or skills/
[x] Delete .omp/APPEND_SYSTEM.md

Next:
- Replace the placeholder URL in .gitmodules with the real remote for toolkit/.
- Push the toolkit/ submodule to its remote, then run `git submodule update --init`.
- Update ~/.hermes/config.yaml as noted above.