docs, messages: Resolve nixos.org/manual/nix/stable redirect

Loads a bit quicker

src/libstore-c/nix_api_store.h

@@ -57,14 +57,14 @@ nix_err nix_libstore_init_no_load_config(nix_c_context * context);
  * ignores `NIX_REMOTE` and the `store` option. For this reason, `NULL` is most likely the better choice.
  *
  *   For supported store URLs, see [*Store URL format* in the Nix Reference
- * Manual](https://nixos.org/manual/nix/stable/store/types/#store-url-format).
+ * Manual](https://nix.dev/manual/nix/stable/store/types/#store-url-format).
  * @endparblock
  *
  * @param[in] params @parblock
  *   optional, null-terminated array of key-value pairs, e.g. {{"endpoint",
  * "https://s3.local"}}.
  *
- *   See [*Store Types* in the Nix Reference Manual](https://nixos.org/manual/nix/stable/store/types).
+ *   See [*Store Types* in the Nix Reference Manual](https://nix.dev/manual/nix/stable/store/types).
  * @endparblock
  *
  * @return a Store pointer, NULL in case of errors

src/nix/nix.md

@@ -44,7 +44,7 @@ R""(
 Nix is a tool for building software, configurations and other
 artifacts in a reproducible and declarative way. For more information,
 see the [Nix homepage](https://nixos.org/) or the [Nix
-manual](https://nixos.org/manual/nix/stable/).
+manual](https://nix.dev/manual/nix/stable/).
 
 # Installables