nixos/seerr: change default path to match new naming

- Only change paths on major version change.
- Add breaking change note to release notes.

Signed-off-by: Nicolas Dumazet <nicdumz.commits@gmail.com>

nixos/doc/manual/release-notes/rl-2605.section.md

@@ -211,7 +211,10 @@ See <https://github.com/NixOS/nixpkgs/issues/481673>.
 
 - `geph` package's built-in GUI `geph5-client-gui` has been [removed](https://github.com/geph-official/geph5/commit/f2221fb8386312daf2cef05483ebb353ff48bdb4) by the upstream. All users who wish to continue using the GUI should install the `gephgui-wry`, which is consistent with the official release version.
 
-- `services.jellyseerr` has been renamed to `services.seerr` following the upstream changes. Service name changed accordingly.
+- `services.jellyseerr` has been renamed to `services.seerr` following the upstream changes. Notable breaking changes:
+  - systemd service name changed accordingly.
+  - Default config directory moved from `/var/lib/jellyseerr/config` to `/var/lib/seerr/`.
+    - If `stateVersion` is older than `26.05`, the module fall backs to the legacy path value.
 
 - `services.vikunja` has been updated to Vikunja [v1.0.0](https://vikunja.io/changelog/whats-new-in-vikunja-1.0.0/), which introduces multiple breaking changes.
   Notable breaking changes:

nixos/modules/services/misc/seerr.nix

@@ -6,6 +6,9 @@
 }:
 let
   cfg = config.services.seerr;
+  # 26.05 introduced a breaking change which is guarded behind stateVersion to avoid
+  # breaking users.
+  useNewConfigLocation = lib.versionAtLeast config.system.stateVersion "26.05";
 in
 {
   imports = [
@@ -35,7 +38,7 @@ in
 
     configDir = lib.mkOption {
       type = lib.types.path;
-      default = "/var/lib/jellyseerr/config";
+      default = if useNewConfigLocation then "/var/lib/seerr/" else "/var/lib/jellyseerr/config";
       description = "Config data directory";
     };
   };
@@ -51,7 +54,8 @@ in
       };
       serviceConfig = {
         Type = "exec";
-        StateDirectory = "jellyseerr";
+        # Note: this should be a parent of configDir.
+        StateDirectory = if useNewConfigLocation then "seerr" else "jellyseerr";
         DynamicUser = true;
         ExecStart = lib.getExe cfg.package;
         Restart = "on-failure";