feat: use TOML for editable color configuration

Sources/Conjure/ColorScheme.swift

@@ -1,4 +1,5 @@
 import AppKit
+import TOMLDecoder
 
 @MainActor
 struct ColorScheme {
@@ -31,7 +32,7 @@ struct ColorScheme {
     }
 
     static func load(from directory: URL) throws -> ColorScheme {
-        let configURL = directory.appendingPathComponent("config.json")
+        let configURL = directory.appendingPathComponent("config.toml")
         guard let config = try readObject(at: configURL, missingAllowed: true) else { return sunset }
         try validateKeys(config, allowed: ["theme", "colors"], at: configURL, prefix: "")
         let theme: String
@@ -69,7 +70,7 @@ struct ColorScheme {
     private mutating func applyColors(from object: [String: Any], at url: URL) throws {
         guard let value = object["colors"] else { return }
         guard let colors = value as? [String: Any] else {
-            throw ColorSchemeError(path: url.path, reason: "colors must be an object.")
+            throw ColorSchemeError(path: url.path, reason: "colors must contain named color values.")
         }
         try Self.validateKeys(colors, allowed: Set(Self.colorFields.keys), at: url, prefix: "colors.")
         for (name, value) in colors {
@@ -107,10 +108,13 @@ struct ColorScheme {
             throw ColorSchemeError(path: url.path, reason: error.localizedDescription)
         }
         let value: Any
+        let isTOML = url.pathExtension == "toml"
         do {
+            if isTOML { return try Dictionary(TOMLTable(source: data)) }
             value = try JSONSerialization.jsonObject(with: data, options: [.fragmentsAllowed])
         } catch {
-            throw ColorSchemeError(path: url.path, reason: "Invalid JSON: \(error.localizedDescription)")
+            let detail = isTOML ? String(describing: error) : error.localizedDescription
+            throw ColorSchemeError(path: url.path, reason: "Invalid \(isTOML ? "TOML" : "JSON"): \(detail)")
         }
         guard let object = value as? [String: Any] else {
             throw ColorSchemeError(path: url.path, reason: "Expected a JSON object.")