Refactor project configuration to use .json format

- Replaced the legacy .json5 project file with a new .json format for `plugin.project.json`.
- Updated `build.rs` to prioritize the new .json format while maintaining backward compatibility with .json5.
- Made adjustments to the Confirming.lua file to enhance UI consistency.
- Improved metadata handling in snapshot middleware to support both modern and legacy file extensions.

src/syncback/file_names.rs

@@ -38,7 +38,9 @@ pub fn name_for_inst<'old>(
             | Middleware::CsvDir
             | Middleware::ServerScriptDir
             | Middleware::ClientScriptDir
-            | Middleware::ModuleScriptDir => {
+            | Middleware::ModuleScriptDir
+            | Middleware::LocalScriptDir
+            | Middleware::LegacyScriptDir => {
                 let name = if encode_invalid_chars {
                     let encoded = encode_path_name(&new_inst.name);
                     // Validate for issues not fixed by encoding (trailing space/dot, control chars, reserved names)

src/syncback/snapshot.rs

@@ -306,7 +306,14 @@ impl<'sync> SyncbackSnapshot<'sync> {
 
 pub fn filter_out_property(inst: &Instance, prop_name: &str) -> bool {
     match inst.class.as_str() {
-        "Script" | "LocalScript" | "ModuleScript" => {
+        "Script" => {
+            // These properties shouldn't be set by scripts that are created via
+            // `$path` or via being on the file system.
+            // RunContext is filtered because it's encoded in the file extension:
+            // .server.luau → Server, .client.luau → Client, .plugin.luau → Plugin, .legacy.luau → Legacy
+            prop_name == "Source" || prop_name == "ScriptGuid" || prop_name == "RunContext"
+        }
+        "LocalScript" | "ModuleScript" => {
             // These properties shouldn't be set by scripts that are created via
             // `$path` or via being on the file system.
             prop_name == "Source" || prop_name == "ScriptGuid"