opencode: fix config file location

The file should be named `opencode.json`, not `config.json`.

Docs: https://opencode.ai/docs/config/#global

@moduon MT-13030

modules/programs/opencode.nix

@@ -80,7 +80,7 @@ in
         }
       '';
       description = ''
-        Configuration written to {file}`$XDG_CONFIG_HOME/opencode/config.json`.
+        Configuration written to {file}`$XDG_CONFIG_HOME/opencode/opencode.json`.
         See <https://opencode.ai/docs/config/> for the documentation.
 
         Note, `"$schema": "https://opencode.ai/config.json"` is automatically added to the configuration.
@@ -336,7 +336,7 @@ in
     home.packages = mkIf (cfg.package != null) [ cfg.package ];
 
     xdg.configFile = {
-      "opencode/config.json" = mkIf (cfg.settings != { } || transformedMcpServers != { }) {
+      "opencode/opencode.json" = mkIf (cfg.settings != { } || transformedMcpServers != { }) {
         source =
           let
             # Merge MCP servers: transformed servers + user settings, with user settings taking precedence
@@ -345,7 +345,7 @@ in
             mergedSettings =
               cfg.settings // (lib.optionalAttrs (mergedMcpServers != { }) { mcp = mergedMcpServers; });
           in
-          jsonFormat.generate "config.json" (
+          jsonFormat.generate "opencode.json" (
             {
               "$schema" = "https://opencode.ai/config.json";
             }

tests/modules/programs/opencode/empty-settings.nix

@@ -4,6 +4,6 @@
     settings = { };
   };
   nmt.script = ''
-    assertPathNotExists home-files/.config/opencode/config.json
+    assertPathNotExists home-files/.config/opencode/opencode.json
   '';
 }

tests/modules/programs/opencode/mcp-integration-with-override.nix

@@ -41,8 +41,8 @@
   };
 
   nmt.script = ''
-    assertFileExists home-files/.config/opencode/config.json
-    assertFileContent home-files/.config/opencode/config.json \
+    assertFileExists home-files/.config/opencode/opencode.json
+    assertFileContent home-files/.config/opencode/opencode.json \
       ${./mcp-integration-with-override.json}
   '';
 }

tests/modules/programs/opencode/mcp-integration.nix

@@ -29,8 +29,8 @@
   };
 
   nmt.script = ''
-    assertFileExists home-files/.config/opencode/config.json
-    assertFileContent home-files/.config/opencode/config.json \
+    assertFileExists home-files/.config/opencode/opencode.json
+    assertFileContent home-files/.config/opencode/opencode.json \
       ${./mcp-integration.json}
   '';
 }

tests/modules/programs/opencode/settings.nix

@@ -9,8 +9,8 @@
     };
   };
   nmt.script = ''
-    assertFileExists home-files/.config/opencode/config.json
-    assertFileContent home-files/.config/opencode/config.json \
-      ${./config.json}
+    assertFileExists home-files/.config/opencode/opencode.json
+    assertFileContent home-files/.config/opencode/opencode.json \
+      ${./opencode.json}
   '';
 }