gitignore: exclude .cortexkit agent working state

QTA enumerated all 26 CortexKit repos after their gather artifacts rode
into commons PR #15: 24 ignored .cortexkit, two did not (commons,
entorhinal) -- the fixed-the-instances-never-enumerated-the-population
shape in a hygiene pass. A committed context package is the
drifted-evidence class: it wears a source-adjacent path and answers
searches with a different repo's facts.

Author: ualtinok

.gitignore

@@ -2,3 +2,7 @@
 **/*.rs.bk
 Cargo.lock
 .DS_Store
+
+# Agent working state (context packages, prompts, drafts) -- never source.
+# A committed gather artifact answers searches with another repo's details.
+.cortexkit/