chore: gitignore gsd-session-*.html dumps

These are session exports that land at the repo root and should not
be tracked. The .gsd directory is already ignored; this covers the
stray HTML files produced alongside it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -12,6 +12,7 @@ trace-*.out
 
 # ── GSD baseline (auto-generated) ──
 .gsd
+gsd-session-*.html
 .DS_Store
 Thumbs.db
 *.swp