chore: remove accidentally committed .bak and .chronomemory runtime files

specsmith upgrade --full migration created backup (.bak) files and
.chronomemory/events.wal which were accidentally staged. Removing from
index and adding patterns to .gitignore.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: tbitcs

.gitignore

@@ -37,3 +37,12 @@ west-env.local.yml
 
 # ---- Local Python tool artifacts ----
 uv.lock
+
+# specsmith migration backups — regeneratable, never commit
+*.bak
+.specsmith/*.bak
+docs/governance/*.bak
+docs/*.bak
+
+# ChronoMemory ESDB runtime files — regenerated automatically
+.chronomemory/