v0.15.0 (#3627)

Also updates the README to:
 - highlight Dendrite is in maintenance mode
- remove references to being "scalable" as we eventually decided to
focus on smaller deployments not huge ones.
- remove the progress section as it was horribly outdated and in general
Dendrite is roughly feature complete with synapse (with the exception of
sliding sync and OIDC, which is also now mentioned explicitly)

CHANGES.md

@@ -1,5 +1,25 @@
 # Changelog
 
+## Dendrite 0.15.0 (2025-08-12)
+
+### ⚠ Important
+
+This is a security release, adding support for [room version 12](https://matrix.org/blog/2025/08/security-release/).
+
+### Features
+ - Add support for [MSC4163](https://github.com/matrix-org/matrix-spec-proposals/pull/4163).
+ - Add support for [MSC3967](https://github.com/matrix-org/matrix-spec-proposals/pull/3967).
+ - Add support for room version 12.
+
+### Bug fixes
+ - Refactored NATS JetStream code to gracefully handle more potential errors. (contributed by [neilalexander](https://github.com/neilalexander))
+ - Refactored NATS startup and readiness checking. (contributed by [neilalexander](https://github.com/neilalexander))
+ - Updated NATS to 2.11.7. (contributed by [neilalexander](https://github.com/neilalexander))
+ - Fixed an issue which could cause Dendrite to become unresponsive for minutes at a time. (contributed by [viviicat](https://github.com/viviicat))
+ - Order events when backfilling to reduce the amount of unecessary `/state_ids` requests.
+ - Gracefully handle incorrect sync filter JSON.
+ - Fixed an issue which prevented device deletion working correctly. (contributed by [robinsdan](https://github.com/robinsdan))
+
 ## Dendrite 0.14.1 (2025-01-16)
 
 ### ⚠ Important