Miscellaneous fixes (#23082)

* openvino log message and preview directory checks

* restrict config vars for viewer users

* recording timestamp fix

when startTime is exactly on an hour boundary, findIndex returns the first matching chunk, which is the previous hour's chunk (where before == startTime), instead of the correct chunk (where after == startTime)

the bug shows up when using the share timestamp feature and sharing a specific timestamp on the exact hour mark. when accessing the shared link, the timeline would jump to the incorrect hour

* use helper for chunked time range

* Adjustments to contributing docs

* tweak

* Improve wording

* tweak

---------

Co-authored-by: Nicolas Mowen <nickmowen213@gmail.com>

frigate/output/preview.py

@@ -361,14 +361,17 @@ class PreviewRecorder:
             small_frame,
             cv2.COLOR_YUV2BGR_I420,
         )
-        cv2.imwrite(
-            get_cache_image_name(self.camera_name, frame_time),
+        cache_path = get_cache_image_name(self.camera_name, frame_time)
+
+        if not cv2.imwrite(
+            cache_path,
             small_frame,
             [
                 int(cv2.IMWRITE_WEBP_QUALITY),
                 PREVIEW_QUALITY_WEBP[self.config.record.preview.quality],
             ],
-        )
+        ):
+            logger.error("Failed to write preview frame to %s", cache_path)
 
     def write_data(
         self,