Improve MindSpace visual editor UX and default RMB billing.

Add color-coded edit highlights with an in-preview legend, strip CSP meta
for srcdoc editing, and simplify fullscreen preview to immersive visual edit
only. Default billing to CNY token rates unless H5_USE_BACKEND_COST=1.

Co-authored-by: Cursor <cursoragent@cursor.com>

billing.test.mjs

@@ -39,3 +39,16 @@ test('computeDeltaCostCents returns zero when no usage delta', () => {
   });
   assert.equal(computeDeltaCostCents(previous, current, config), 0);
 });
+
+test('computeDeltaCostCents ignores backend USD cost unless explicitly enabled', () => {
+  const previous = { lastInputTokens: 0, lastOutputTokens: 0, lastAccumulatedCost: 0.01 };
+  const current = normalizeTokenState({
+    accumulatedInputTokens: 1000,
+    accumulatedOutputTokens: 500,
+    accumulatedCost: 0.02,
+  });
+  const rmbConfig = { ...config, useBackendCost: false };
+  assert.equal(computeDeltaCostCents(previous, current, rmbConfig), 5);
+  const usdConfig = { ...config, useBackendCost: true };
+  assert.equal(computeDeltaCostCents(previous, current, usdConfig), 8);
+});