Add Emscripten shell and pre-JS for browser compatibility

- src/shell.html: Custom HTML shell with crisp pixel CSS
  (image-rendering: pixelated) and zoom prevention on canvas
- src/emscripten_pre.js: Patches browser quirks that cause crashes:
  - Intercepts resize/scroll events to ensure e.detail is always 0
  - Wraps window properties (innerWidth, outerWidth, etc.) to
    always return integers, fixing browser zoom crashes
- CMakeLists.txt: Output as .html, include shell and pre-js files

The pre-JS fix addresses "attempt to write non-integer (undefined)
into integer heap" errors that occurred when users zoomed the browser
via Ctrl+scroll or browser menu.

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

CMakeLists.txt

@@ -269,6 +269,10 @@ if(EMSCRIPTEN)
         --preload-file=${CMAKE_SOURCE_DIR}/src/scripts@/scripts
         # Preload assets
         --preload-file=${CMAKE_SOURCE_DIR}/assets@/assets
+        # Use custom HTML shell for crisp pixel rendering
+        --shell-file=${CMAKE_SOURCE_DIR}/src/shell.html
+        # Pre-JS to fix browser zoom causing undefined values in events
+        --pre-js=${CMAKE_SOURCE_DIR}/src/emscripten_pre.js
     )
 
     # Add SDL2 options if using SDL2 backend
@@ -288,6 +292,9 @@ if(EMSCRIPTEN)
 
     target_link_options(mcrogueface PRIVATE ${EMSCRIPTEN_LINK_OPTIONS})
 
+    # Output as HTML to use the shell file
+    set_target_properties(mcrogueface PROPERTIES SUFFIX ".html")
+
     # Set Python home for the embedded interpreter
     target_compile_definitions(mcrogueface PRIVATE
         MCRF_WASM_PYTHON_HOME="/lib/python3.14"