Add security notes with safer password changes entry

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

SECURITY_NOTES.md

@@ -0,0 +1,18 @@
+# Security Notes
+
+User-facing notes on security-relevant changes to Probo. For the
+vulnerability reporting process, see [SECURITY.md](SECURITY.md).
+
+## Safer Password Changes
+
+_2026-04-29 — **IAM**_
+
+> Changing or resetting a password now revokes old sessions automatically.
+
+Changing a password should close the door behind it. Probo now revokes existing sessions when credentials change.
+
+If you change your password while signed in, every other active session is expired and your current session stays open. If your password is reset, all sessions are expired.
+
+It is a small security detail, but an important one. A password update now does what people expect: it cuts off old access immediately.
+
+Thanks to [emimoir](https://github.com/emimoir) for reporting the security issue behind this fix.