docs: update latest checkpoint tag to v2026.9.8

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -16,7 +16,7 @@ OrbitHub is in active development.
 - Milestones completed: M0-M5, and M7-M9
 - Current milestone: Milestone 10 (v1.0 Stabilization)
 - Deferred milestone: Milestone 6 (VNC Fully Working)
-- Latest checkpoint tag: `v0-m9-done`
+- Latest checkpoint tag: `v2026.9.8`
 - VNC implementation milestone (M6) is currently deferred
 
 Progress and milestone details: