gitignore: add rejoin-launch.md + NOTES.md + TODO.md

Local-only notes at the project root stay local. Adds a belt-and-
suspenders safeguard after the LAUNCH.md incident — these common
local-scratch filenames are now explicitly excluded.

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

Author: Brian Akaka

.gitignore

@@ -12,3 +12,8 @@ dist/
 *.egg-info/
 .pytest_cache/
 .ruff_cache/
+
+# local notes — never commit
+rejoin-launch.md
+NOTES.md
+TODO.md