SkillService: enable/disable (persisted in skill_states table, schema
v4), import from YAML (with path traversal + name validation), reload
from file, update config. GET /skills now filters disabled skills.
KbService: list/upload/delete documents with department_id binding.
Added department_id field to KnowledgeSource + UploadedDocument.
Department visibility: (bound to user depts) ∪ (global = None).
10 new admin endpoints: skill enable/disable/import/reload/update,
KB documents CRUD, source sync/rebuild. All guarded by _require_admin.
Implemented reload stub in skill_management.py (was no-op).
54 new tests (26 unit + 28 integration). Fixed 4 pre-existing lint
errors. 357 admin tests pass, no regressions.
chiguyong