add sandbox support to desktop designer, fix mouse coordinates and UI issues

- Add DesktopSandbox class that integrates timer, JSON, crypto, and VirtualFS APIs
- Fix mouse coordinate handling: GLFW reports window coordinates, not physical pixels
- Fix font path resolution to search multiple locations for test apps
- Fix screenshot capture timing (capture before buffer swap)
- Fix test app CSS: use border-width instead of border:none, add display:block
- Fix test app Lua: add document nil checks, use HTML entities for symbols
- Update hot_reload to reset sandbox state on reload

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test-apps/com.mosis.sandbox-test/styles.rcss

@@ -3,6 +3,8 @@ body {
     font-size: 16dp;
     background-color: #121212;
     color: #ffffff;
+    width: 100%;
+    height: 100%;
 }
 
 .app-bar {
@@ -38,10 +40,14 @@ body {
 }
 
 .content {
+    display: block;
     padding: 16dp;
+    width: auto;
+    box-sizing: border-box;
 }
 
 .card {
+    display: block;
     background-color: #1e1e1e;
     border-radius: 12dp;
     padding: 16dp;
@@ -49,16 +55,22 @@ body {
 }
 
 .card-title {
+    display: block;
     font-size: 18dp;
     font-weight: bold;
     margin-bottom: 8dp;
     color: #bb86fc;
 }
 
+.card div {
+    display: block;
+}
+
 button {
+    display: block;
     background-color: #bb86fc;
     color: #000000;
-    border: none;
+    border-width: 0;
     border-radius: 8dp;
     padding: 12dp 24dp;
     font-size: 14dp;
@@ -75,7 +87,7 @@ button:active {
 }
 
 #results {
-    font-family: monospace;
+    font-family: LatoLatin;
     font-size: 12dp;
     background-color: #0d0d0d;
     padding: 12dp;