Dashboard patch state: kept until cleanup --all; frame-controls v6

The policy for the `state = true` files
(~/.local/state/steam-frame-nix/ui-patches/<name>.json), now stated in the
option, the injector and the README: they are user data, kept when a patch
is disabled or removed (the choices come back when it is enabled again),
and removed only by `steam-frame-nix-cleanup --all` / `install.sh
uninstall`; `--orphans` removes stale *.json.tmp only.

frame-controls v6 drops v5's one-time read of version 4's localStorage copy:
steamvr.service deletes ~/.cache/SteamVR (and with it that localStorage) on
every SteamVR start, so there is nothing left to migrate.

README.md

@@ -330,8 +330,10 @@ binding `window.__sfuiStoreSave`; the service writes the file atomically,
 only on change, only for that page's `state` patches, at most 64 KiB. Used
 by the [window control bar](#window-control-bar-dashboardframecontrols)
 and the [Steam close button](#steam-close-button-dashboardsteamclosebuttonenable).
-The file is user data, not generated by Nix; see
-[Changes outside Nix](#changes-outside-nix).
+The file is user data, not generated by Nix: it is kept when the patch is
+disabled or removed (the choices come back when you enable it again) and
+removed only by `steam-frame-nix-cleanup --all` or `install.sh uninstall`;
+see [Changes outside Nix](#changes-outside-nix).
 
 **DevTools on the LAN:** Steam's Developer Mode enables
 `steam-web-debug-portforward` (`0.0.0.0:8081` → `8080`) and
@@ -764,8 +766,7 @@ controller), and theater windows have no "Float".
   popup moves that control between bar and menu **for all windows**.
   Placements survive SteamVR restarts and reboots (saved in
   `~/.local/state/steam-frame-nix/ui-patches/frame-controls.json`, see
-  [persistent state](#ui-patches-uipatchespatches); version 4 kept them in
-  localStorage, which SteamVR wipes on every start, and is migrated once).
+  [persistent state](#ui-patches-uipatchespatches)).
 - `inBar` / `inMenu` set where controls start; a popup choice wins until
   that control's entry changes.
 - `floatInTheater` gives theater windows the "Float" control.
@@ -930,7 +931,7 @@ the feature off:
 
 | Path | What, why | Cleanup |
 |---|---|---|
-| `~/.local/state/steam-frame-nix/ui-patches/<name>.json` | Choices made in the dashboard: window control bar placements (`frame-controls.json`), "Steam hidden" (`steam-close-button.json`). Written by `steam-ui-patches` because SteamOS's `steamvr.service` deletes `~/.cache/SteamVR` (the dashboard's own browser storage) on every SteamVR start. Kept when a feature is disabled (your choices come back when you re-enable it). | `rm -rf ~/.local/state/steam-frame-nix/ui-patches` (also done by `install.sh uninstall`) |
+| `~/.local/state/steam-frame-nix/ui-patches/<name>.json` | Choices made in the dashboard: window control bar placements (`frame-controls.json`), "Steam hidden" (`steam-close-button.json`). Written by `steam-ui-patches` because SteamOS's `steamvr.service` deletes `~/.cache/SteamVR` (the dashboard's own browser storage) on every SteamVR start. Kept when a feature is disabled (your choices come back when you re-enable it). | `steam-frame-nix-cleanup --all` (also run by `install.sh uninstall`) |
 
 ## Rollback