feat(ecg): add DICOM ECG waveform extension (#5856)

* feat(ecg): add DICOM ECG waveform extension

Introduce @ohif/extension-dicom-ecg for rendering DICOM waveform (ECG)
data. Register the extension in the basic mode and pluginConfig.json,
and remove ECG from NON_IMAGE_MODALITIES so waveform display sets are
handled by the new viewport.

* refactor(ecg): move ECG support into cornerstone extension per review feedback

- Remove standalone dicom-ecg extension; fold all ECG functionality into
  the cornerstone extension as requested by reviewer
- Add ECG SOP class handler (DicomEcgSopClassHandler) to the cornerstone
  extension getSopClassHandlerModule, registering ECG waveform metadata
  via genericMetadataProvider on display set creation
- Move ECG helpers (buildEcgModule, decodeInt16Multiplex, base64ToArrayBuffer)
  into extensions/cornerstone/src/utils/ecgMetadata.ts
- Handle ECGViewport in CornerstoneViewportService._setDisplaySets by
  detecting ECGViewport instanceof and calling setEcg(imageId) directly,
  so OHIFCornerstoneViewport can be used without a custom ECG viewport component
- Add ECG support to getCornerstoneViewportType utility
- Update basic mode to reference the cornerstone extension's ECG SOP handler
  and use the base cornerstone viewport for ECG display sets
- Migrate ecgMetadata and getCornerstoneViewportType tests

* chore: revert bun.lock to upstream origin/master

---------

Co-authored-by: Bill Wallace <wayfarer3130@gmail.com>

README.md

@@ -49,6 +49,7 @@ provided by the <a href="https://ohif.org/">Open Health Imaging Foundation (OHIF
 | <img src="https://github.com/OHIF/Viewers/blob/master/platform/docs/docs/assets/img/demo-4d.webp?raw=true" alt="4D" width="350"/> | 4D  | [Demo](https://viewer.ohif.org/dynamic-volume?StudyInstanceUIDs=2.25.232704420736447710317909004159492840763) |
 | <img src="https://github.com/OHIF/Viewers/blob/master/platform/docs/docs/assets/img/demo-video.webp?raw=true" alt="VIDEO" width="350"/> | Video  | [Demo](https://viewer.ohif.org/viewer?StudyInstanceUIDs=2.25.96975534054447904995905761963464388233) |
 | <img src="https://github.com/OHIF/Viewers/blob/master/platform/docs/docs/assets/img/microscopy.webp?raw=true" alt="microscopy" width="350"/> | Slide Microscopy  | [Demo](https://viewer.ohif.org/microscopy?StudyInstanceUIDs=2.25.141277760791347900862109212450152067508) |
+| <img src="https://github.com/OHIF/Viewers/blob/master/platform/docs/docs/assets/img/demo-ecg.webp?raw=true" alt="ECG" width="350"/> | ECG Waveform  | [Demo](https://viewer-dev.ohif.org/viewer?StudyInstanceUIDs=2.25.209974489360710696739324151261716440238) |
 
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