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/output.py

@@ -349,6 +349,13 @@ def move_preview_frames(loc: str) -> None:
             if not os.path.exists(preview_holdover):
                 return
 
+            if not os.access(preview_holdover, os.R_OK | os.W_OK):
+                logger.error(
+                    "Insufficient permissions on preview restart cache at %s",
+                    preview_holdover,
+                )
+                return
+
             shutil.move(preview_holdover, preview_cache)
     except shutil.Error:
         logger.error("Failed to restore preview cache.")