chore: untrack ruvector.db runtime artifacts + gitignore at any depth

These are hook/runtime-generated databases (ruvector/intelligence store)
that kept showing as dirty and don't belong in version control. Removed
from the index (files kept on disk) and ignored globally.

Co-Authored-By: claude-flow <ruv@ruv.net>

.gitignore

@@ -287,3 +287,7 @@ harness/**/*.tgz
 harness/**/package-lock.json
 harness/**/.claude-flow/
 harness/**/ruvector.db
+
+# ruvector runtime/hook DB — never tracked (any depth)
+ruvector.db
+**/ruvector.db