Document today's restructures, and give data/ a README that ships with it

Plugin/unraid/Tools/README-Tools.md

@@ -23,7 +23,7 @@ containers, VMs, transcodes, arr library counts. Building that live on every pag
 dozens of API calls and `docker inspect` runs per refresh, from a WebGUI that is already the
 first thing to slow down under load.
 
-Instead, both are written to `/tmp/vv_cache` (tmpfs — RAM-speed reads, cleared on reboot) and
+Instead, both are written to `$VV_CACHE_DIR` (`/tmp/varaverk/api`, tmpfs — RAM-speed reads, cleared on reboot) and
 the pages serve from there.
 
 ### ⚡  `api_cache_writer.sh` — local payloads, every minute
@@ -128,7 +128,7 @@ that prevents shadow directories.
                                   │
   Tools/api_cache_writer.php ─────┘   same builders → cache can't disagree with live
         │
-        └─► /tmp/vv_cache/monitor.json ──► served by api/monitor.php unless ?live=1
+        └─► /tmp/varaverk/api/monitor.json ──► served by api/monitor.php unless ?live=1
 ```
 
 Adding a metric means adding it in `include/` once. The page, the live endpoint, and the cache