chore(gitignore): ignore generated .verisim/ sidecar artifacts (#154)

Salvage the .gitignore tidy from claude/gracious-curie-HS03A: ignore the
generated .verisim/ sidecar artifacts (stores, `generate` scaffolds, and
`<path>.lock` write-locks from the V-L2-F3/F4 JSON sidecar work). Verified
no tracked files live under .verisim/. No source/code change.

https://claude.ai/code/session_01Ux144vBDdySvLUqUrCgkT4

Author: hyperpolymath

.gitignore

@@ -92,6 +92,12 @@ docs/reports/maintenance/*.json
 *.tmp
 *.bak
 
+# Generated VeriSimiser sidecar artifacts — stores, `generate` scaffolds, and
+# `<path>.lock` write-locks. The default sidecar/output location is .verisim/
+# (see `[sidecar].path` and `verisimiser generate -o`); these are runtime
+# data, never source. Atomic-write temp files are covered by `*.tmp` above.
+.verisim/
+
 # Crash recovery artifacts
 ai-cli-crash-capture/