remove docs/CHANGES-2026-09.md: one-off audit-batch record, every fix already in the git log with explanatory commits; drop its mention from SPEC milestones

SPEC.md

@@ -184,6 +184,5 @@ shipped since this list was written.) Add when someone asks.
    states, autoplay default, `run.sh`.
 7. Auth — login screen, then multi-user CLI-created accounts with
    per-user history + test suite.
-8. Later (see git log, `docs/CHANGES-2026-09.md`): provider layer with
-   hianime primary, SQLite storage, stats/events, 2026-09 security
-   audit batch.
+8. Later (see git log): provider layer with hianime primary, SQLite
+   storage, stats/events, 2026-09 security audit batch.