implement caching for TeslaCam directory scan and add refresh endpoint

README.md

@@ -105,6 +105,7 @@ file / environment rather than relying on `.env`.
 | `/`                      | Main page with all videos categorized by camera view |
 | `/camera/<camera_view>`  | All videos for a single camera view                  |
 | `/video/<path:filepath>` | Streams a video file from the TeslaCam directory     |
+| `/refresh`               | Forces a re-scan of the TeslaCam directory           |
 
 ## Camera Views
 
@@ -119,6 +120,9 @@ file / environment rather than relying on `.env`.
 
 ## Notes
 
+- The directory scan is cached in memory for `SCAN_CACHE_TTL` seconds
+  (default 300) to avoid re-walking the tree on every request. Hit
+  `/refresh` to force a re-scan after copying new clips onto the drive.
 - Debug mode is off by default (`FLASK_DEBUG=0`) and is only used by the local
   dev server. It has no effect when running under a WSGI server like gunicorn.
 - The TeslaCam directory must be accessible from the machine running the app (e.g., a mounted USB drive or network share).