Improve stream UI: grouped sections, full-size preview lightbox, and test redesign

- Separate Screen Capture and Processed streams into grouped sections with headers
- Remove redundant Type dropdown from stream modal (type inferred from add button)
- Add full-resolution image to test endpoints alongside thumbnails
- Add image lightbox with clickable preview for full-size viewing
- Move test results from modal into lightbox overlay with capture stats
- Apply postprocessing to both thumbnail and full image for processed streams
- Rename "Assigned Picture Stream" to "Picture Stream" in device settings
- Fix null reference errors from removed test result HTML elements

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/locales/en.json

@@ -197,8 +197,14 @@
   "common.edit": "Edit",
   "streams.title": "\uD83D\uDCFA Picture Streams",
   "streams.description": "Picture streams define the capture pipeline. A raw stream captures from a display using a capture template. A processed stream applies postprocessing to another stream. Assign streams to devices.",
+  "streams.group.raw": "Screen Capture Streams",
+  "streams.group.processed": "Processed Streams",
   "streams.add": "Add Picture Stream",
+  "streams.add.raw": "Add Screen Capture",
+  "streams.add.processed": "Add Processed Stream",
   "streams.edit": "Edit Picture Stream",
+  "streams.edit.raw": "Edit Screen Capture",
+  "streams.edit.processed": "Edit Processed Stream",
   "streams.name": "Stream Name:",
   "streams.name.placeholder": "My Stream",
   "streams.type": "Type:",
@@ -245,7 +251,7 @@
   "postprocessing.config.show": "Show settings",
   "device.button.stream_selector": "Stream Settings",
   "device.stream_settings.title": "📺 Stream Settings",
-  "device.stream_selector.label": "Assigned Picture Stream:",
+  "device.stream_selector.label": "Picture Stream:",
   "device.stream_selector.hint": "Select a picture stream that defines what this device captures and processes",
   "device.stream_selector.none": "-- No stream assigned --",
   "device.stream_selector.saved": "Stream settings updated",