chore: gitignore var/log/ (#8144)

src/node/updater writes var/log/update.log at runtime (index.ts
logPath(), plus UpdateExecutor and RollbackHandler). var/.gitignore
covers update-state.json but not the log directory, so running the
backend suite leaves an untracked file that `git add -A` will happily
sweep into a commit.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

var/.gitignore

@@ -4,3 +4,5 @@ installed_plugins.json
 dirty.db
 rusty.db
 update-state.json
+# Runtime update log, written by src/node/updater (see index.ts logPath()).
+log/