docs: document the /romm/sync mount and the new download cache location

docs/administration/library-conversion.md

@@ -100,7 +100,7 @@ Any format rom-converto can reach from the stored file is allowed here, lossy on
 
 ### The conversion cache
 
-Converted downloads are cached in `/romm/cache/converts`. A copy expires `cache_ttl_hours` after it was last served, and when the cache would grow past `cache_max_size_gb`, the least recently served copies are evicted first. The **Scheduled conversion cache cleanup** task removes expired copies every day at 04:00. A conversion that failed is remembered, so it isn't retried on every request until its cache entry expires.
+Converted downloads are cached inside the container at `/tmp/romm/cache/converts`, or `$ROMM_TMP_PATH/cache/converts` when [`ROMM_TMP_PATH`](../reference/environment-variables.md) is set. The cache is cleared when the container is recreated, and converted downloads are rebuilt on demand. With the default `cache_max_size_gb` of 20, a small Docker disk (such as Unraid's `docker.img`) can fill up, so point `ROMM_TMP_PATH` at a mounted host folder if that's a concern. Library conversion writes into the library itself and doesn't use this cache. A copy expires `cache_ttl_hours` after it was last served, and when the cache would grow past `cache_max_size_gb`, the least recently served copies are evicted first. The **Scheduled conversion cache cleanup** task removes expired copies every day at 04:00. A conversion that failed is remembered, so it isn't retried on every request until its cache entry expires.
 
 ## API
 

docs/getting-started/quick-start.md

@@ -41,6 +41,7 @@ You'll want to edit the following values before launching:
 | `romm`    | `/path/to/library` volume | Host path to the directory containing your `roms/` folder.                                           |
 | `romm`    | `/path/to/assets` volume  | Host storage paths for saves, states and screenshots.                                                |
 | `romm`    | `/path/to/config` volume  | Host path to a directory that will hold `config.yml`.                                                |
+| `romm`    | `/path/to/sync` volume    | Only if you enable the sync folder watcher or push/pull sync.                                        |
 
 Generate the auth secret now so you don't forget:
 

docs/install/backup-and-restore.md

@@ -14,6 +14,7 @@ This page covers routine backups and restoring from them.
 | **Database** (`mysql_data`, `pg_data`, etc.) | User accounts, ROM metadata, collections, ratings, play sessions, paired devices, saves/states metadata | **Critical**: back this up nightly.                                                                  |
 | **`/romm/assets`**                           | User uploads: save files, save states, user-uploaded screenshots, manuals, covers                       | **Critical**: back this up nightly.                                                                  |
 | **`/romm/config`**                           | `config.yml` and any custom overrides                                                                   | **Critical**: rarely changes but small and painful to recreate.                                      |
+| `/romm/sync`                                 | SSH keys, `known_hosts` and incoming device files, when the sync features are enabled                   | **Critical** if you use sync: keys are painful to recreate and re-register on every device.          |
 | `/romm/resources`                            | Metadata images (covers, screenshots) fetched from IGDB/ScreenScraper/etc.                              | Medium priority, and can be re-downloaded on a rescan (including it speeds up recovery).             |
 | `/redis-data`                                | Task queue state                                                                                        | Low priority, in-flight tasks only, and lost tasks can be re-run.                                    |
 | **`/romm/library`**                          | Your ROM files                                                                                          | Back this up separately. It's your source data and you should already have a backup strategy for it. |

docs/install/unraid.md

@@ -16,6 +16,10 @@ Both end up with the same running stack.
 !!! warning "Back up `appdata` before updates"
     Tearing down the container wipes its resources directory (covers, screenshots, cached metadata). Mount `appdata` on a safe path or [back it up](backup-and-restore.md) before every upgrade.
 
+<!-- prettier-ignore -->
+!!! note "Only mounted paths are writable"
+    Containers on Unraid usually run as `99:100` (`nobody:users`), which can only write to the paths you map. If you enable `ENABLE_SYNC_FOLDER_WATCHER` or `ENABLE_SYNC_PUSH_PULL`, add a path mapping for `/romm/sync`, or the sync folder watcher stays off. Download caches live in `/tmp/romm/cache` inside `docker.img`; set `ROMM_TMP_PATH` to a mapped folder to keep them off it.
+
 ---
 
 ## Community Apps template

docs/resources/snippets/quick-start.docker-compose.yml

@@ -27,6 +27,7 @@ services:
             - /path/to/library:/romm/library # Your game library. Check https://github.com/rommapp/romm?tab=readme-ov-file#folder-structure for more details.
             - /path/to/assets:/romm/assets # Uploaded saves, states, etc.
             - /path/to/config:/romm/config # Path where config.yml is stored
+            # - /path/to/sync:/romm/sync # Required for ENABLE_SYNC_FOLDER_WATCHER and ENABLE_SYNC_PUSH_PULL
         ports:
             - 80:8080
         depends_on: