fix(flutter): handle nested colors split in tokens.json codegen

Web tokens.json was reshaped for the SPA theme toggle (#362) with
colors split into dark/light/flat blocks. gen_tokens.dart still
expected a flat string map and threw _Map<String,dynamic> cast
errors in the flutter CI workflow. Read colors.dark + colors.flat
and merge into the existing flat namespace; light variants will be
emitted when the Flutter client gains a theme toggle as part of
#356 parity work. Adds hyphen→camelCase normalization so the new
on-action token surfaces as onAction.

flutter_client/lib/theme/tokens.dart

@@ -17,6 +17,7 @@ class FabledSwordTokens {
   static const Color error = Color(0xFFC04A1F);
   static const Color info = Color(0xFF3D5A6E);
   static const Color accent = Color(0xFF4A6B5C);
+  static const Color onAction = Color(0xFFE8E4D8);
   static const double radiusSm = 4;
   static const double radiusMd = 8;
   static const double radiusLg = 12;

flutter_client/shared/fabledsword.tokens.json

@@ -1,31 +1,36 @@
 {
   "colors": {
+    "dark": {
       "obsidian": "#14171A",
       "iron": "#1E2228",
       "slate": "#2C313A",
       "pewter": "#3F4651",
       "parchment": "#E8E4D8",
       "vellum": "#C2BFB4",
-    "ash": "#9C9A92",
+      "ash": "#9C9A92"
+    },
+    "light": {
+      "obsidian": "#F8F5EE",
+      "iron": "#ECE6D5",
+      "slate": "#DCD3BD",
+      "pewter": "#B8AE94",
+      "parchment": "#14171A",
+      "vellum": "#2C313A",
+      "ash": "#5C6068"
+    },
+    "flat": {
       "moss": "#4A5D3F",
       "bronze": "#8B7355",
       "oxblood": "#6B2118",
       "warning": "#8B6F1E",
       "error": "#C04A1F",
       "info": "#3D5A6E",
-    "accent": "#4A6B5C"
-  },
-  "radii": {
-    "sm": "4px",
-    "md": "8px",
-    "lg": "12px",
-    "xl": "16px"
-  },
-  "fonts": {
-    "display": "Fraunces",
-    "body": "Inter",
-    "mono": "JetBrains Mono"
+      "accent": "#4A6B5C",
+      "on-action": "#E8E4D8"
+    }
   },
+  "radii": { "sm": "4px", "md": "8px", "lg": "12px", "xl": "16px" },
+  "fonts": { "display": "Fraunces", "body": "Inter", "mono": "JetBrains Mono" },
   "fontStacks": {
     "display": "'Fraunces', Georgia, serif",
     "body": "'Inter', system-ui, sans-serif",

flutter_client/tool/gen_tokens.dart

@@ -1,13 +1,23 @@
 // Reads shared/fabledsword.tokens.json and emits lib/theme/tokens.dart.
 // Run via `dart run tool/gen_tokens.dart`. The generated file is
 // committed (CI validates it matches the JSON to catch drift).
+//
+// Web tokens.json splits colors into `dark`, `light`, and `flat` blocks
+// for the SPA's theme toggle. Flutter v1 ships dark-only, so we merge
+// dark + flat into a single flat namespace. Light variants will be
+// emitted alongside as part of the Flutter theme-toggle parity work.
 import 'dart:convert';
 import 'dart:io';
 
 void main() {
   final jsonFile = File('shared/fabledsword.tokens.json');
   final tokens = jsonDecode(jsonFile.readAsStringSync()) as Map<String, dynamic>;
-  final colors = (tokens['colors'] as Map).cast<String, String>();
+
+  final colorsRoot = (tokens['colors'] as Map).cast<String, dynamic>();
+  final dark = (colorsRoot['dark'] as Map).cast<String, String>();
+  final flat = (colorsRoot['flat'] as Map).cast<String, String>();
+  final colors = <String, String>{...dark, ...flat};
+
   final radii = (tokens['radii'] as Map).cast<String, String>();
   final fonts = (tokens['fonts'] as Map).cast<String, String>();
 
@@ -38,5 +48,11 @@ void main() {
   stdout.writeln('wrote lib/theme/tokens.dart');
 }
 
-String _camel(String s) => s; // tokens are already lowerCamel-friendly
+// Hyphens become camelCase boundaries: on-action → onAction.
+String _camel(String s) {
+  final parts = s.split('-');
+  return parts.first +
+      parts.skip(1).map((p) => p[0].toUpperCase() + p.substring(1)).join();
+}
+
 String _pascal(String s) => s[0].toUpperCase() + s.substring(1);