docs(migration): explain backups and board scaling (#6991)

* docs(migration): explain backups and board scaling

* docs: qualify migration layout restoration

apps/docs/blog/2026/09-03-homarr-2.0/index.mdx

@@ -43,7 +43,7 @@ Homarr 2.0 builds on the dashboard you already use. Here is what changed.
 
 {/* Historical excerpt boundary. */}
 
-SQLite and PostgreSQL users can update their Homarr image as usual; database migrations run automatically at startup. **MySQL users must convert before upgrading**, as explained below. Workshop uses the production service by default, with no preview URL configuration required.
+**Back up before upgrading:** database migrations run automatically at startup and change the existing database in place. Follow the [upgrade and rollback guidance](/docs/getting-started/installation/docker#update), including the note on board sizing. **MySQL users must convert before upgrading**, as explained below. Workshop uses the production service by default, with no preview URL configuration required.
 
 ## Database support in v2
 

apps/docs/docs/getting-started/installation/docker.mdx

@@ -24,15 +24,44 @@ see [Managing integrations](/docs/management/integrations#configuration).
 
 ### Update
 
+<Alert type="warning">
+**Back up before upgrading from v1 to v2.** v2 migrates the existing database in place. For SQLite, this is
+`/appdata/db/db.sqlite` by default; v1 cannot use the upgraded database. Switching back to the v1 image alone is not a
+rollback. Image-rollback tools that revert only the container image do not restore the database; you still need
+the pre-upgrade backup.
+
+Stop Homarr before copying the complete `/appdata` directory or volume. Keep the pre-upgrade copy, your container
+configuration, and `SECRET_ENCRYPTION_KEY` securely. If you use an external PostgreSQL database, back it up with its
+native tools as well. See [Backup and restore](/docs/management/backup).
+
+</Alert>
+
 Update the image and recreate the container with the same configuration. Homarr runs database migrations automatically
 at startup, including when moving from v1 to v2; no separate upgrade procedure is needed. Keep the `/appdata` mount and
 `SECRET_ENCRYPTION_KEY` unchanged. Workshop connects to the production service by default.
 
+Existing MySQL installations must [convert to SQLite before upgrading to v2](/docs/advanced/mysql-to-sqlite).
+
 ```sh
 docker compose pull
 docker compose up -d
 ```
 
+To roll back, stop v2, restore the **pre-upgrade** database and `/appdata` backup with the matching configuration and
+encryption key, then start the previously used v1 image. A backup taken after v2 has migrated the database cannot
+restore v1 compatibility.
+
+#### Board sizing after upgrading to v2
+
+v2 uses fixed `200 × 200` logical-pixel cells and scales the whole board to fit the available width. A migrated
+12-column layout can therefore show smaller widgets and text than in v1. Reducing the column count in
+[board layout settings](/docs/management/boards#responsive-layouts) makes cells appear larger at the same viewport
+width; choose a count that fits your content.
+
+Back up before changing columns: reducing the count can resize Containers and displace widgets. Check the layout in
+edit mode before saving. In v2.0.0, increasing the count again may not restore the previous arrangement after widgets
+or Containers have been displaced or resized; keep a backup rather than relying on reversing the column change.
+
 ### Uninstall
 
 `docker compose down` removes the containers and Compose network. Delete the configured `/appdata` host directory or
@@ -53,5 +82,6 @@ docker run \
   -d ghcr.io/homarr-labs/homarr:latest
 ```
 
-Remove the Docker socket mount when it is not required. To update, pull the current image, recreate the container with
-the same arguments, and keep the `/appdata` mount and `SECRET_ENCRYPTION_KEY` unchanged.
+Remove the Docker socket mount when it is not required. To update, follow the [backup guidance above](#update), pull
+the current image, recreate the container with the same arguments, and keep the `/appdata` mount and
+`SECRET_ENCRYPTION_KEY` unchanged.

apps/docs/docs/management/boards/index.mdx

@@ -38,8 +38,8 @@ Mobile and Base are protected layouts. New boards use three Mobile columns; Base
 creation. Additional layouts use unique breakpoints. Homarr selects the layout with the highest breakpoint that fits
 the current viewport.
 
-Tiles use fixed `200 × 200` logical-pixel cells with a `24px` gap. Homarr scales the complete layout to the available
-width instead of changing each widget's proportions. **Reset from Base** regenerates a Mobile or custom layout from the
+The logical grid uses fixed `200 × 200` cells with a `12px` gap. Visible tile spacing also depends on card insets and
+canvas scaling. Homarr scales the complete layout to the available width instead of changing each widget's proportions. **Reset from Base** regenerates a Mobile or custom layout from the
 current Base layout.
 
 Changing column or sidebar counts keeps a saved source arrangement while its generated positions remain unedited.