Update diagrams links

CHANGELOG.md

@@ -16,10 +16,10 @@ History: [bf9871e](https://git.himro.ca/deeaitch/ota-reference-design/commit/bf9
 
 ### Diagrams and A/B simulation
 
-- Added three diagrams for chapters 03–05, with editable PlantUML sources and SVG previews:
-  - OTA architecture: [source](diagrams/plantuml/ota-architecture.puml), [preview](diagrams/rendered/ota-architecture.svg).
-  - A/B trial boot, confirmation, and recovery: [source](diagrams/plantuml/ab-trial-boot.puml), [preview](diagrams/rendered/ab-trial-boot.svg).
-  - A/B storage layout: [source](diagrams/plantuml/ab-storage-layout.puml), [preview](diagrams/rendered/ab-storage-layout.svg).
+- Added three diagrams for chapters 03–05, with editable PlantUML sources and PNG previews:
+  - OTA architecture: [source](diagrams/plantuml/ota-architecture.puml), [preview](diagrams/rendered/ota-architecture.png).
+  - A/B trial boot, confirmation, and recovery: [source](diagrams/plantuml/ab-trial-boot.puml), [preview](diagrams/rendered/ab-trial-boot.png).
+  - A/B storage layout: [source](diagrams/plantuml/ab-storage-layout.puml), [preview](diagrams/rendered/ab-storage-layout.png).
 - Added [diagram rendering instructions](diagrams/readme.md) and links from the corresponding chapters.
 - Added a [C++17 A/B trial boot simulation](examples/simulations/ab-trial-boot/readme.md) with six scenarios: successful confirmation, failed health checks, exhausted attempts, restart during trial, interrupted preparation, and recovery failure. The example includes saved boot state, [state and scenario checks](examples/simulations/ab-trial-boot/tests.cpp), and [CMake/CTest integration](examples/simulations/ab-trial-boot/CMakeLists.txt). It models logical transitions assuming valid completed writes; power-loss safety is outside its scope.
 - Linked the practical material from the [README](readme.md) and [series overview](docs/00-series-overview.md).