Implement wxClipboard and add button finder utility for canvas testing

wxClipboard:
- Update wxwidgets submodule with full wxClipboard implementation
- Add clipboard async functions to ASYNCIFY_IMPORTS in Makefile.wasm
- Update clipboard tests with correct button positions
- Add clipboard permissions to playwright config
- Update WHATWORKS.md to mark wxClipboard as working

Button Finder Utility:
- Add parametric button-finder.spec.ts for scanning canvas apps
- Utility scans for clickable buttons by detecting console log responses
- Excluded from regular test runs via testIgnore
- Supports APP_URL, START_Y, END_Y, STEP environment variables
- Document usage in tests/README.md

All 91 tests pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/wasm-app/Makefile.wasm

@@ -31,11 +31,13 @@ endif
 # Base Emscripten flags (for all apps)
 # ASYNCIFY enables blocking modal dialogs (ShowModal waits for user)
 # ASYNCIFY_IMPORTS tells Emscripten which imported JS functions can unwind the stack
+# - startModal: for modal dialogs
+# - js_writeTextToClipboard, js_readTextFromClipboard, js_clipboardHasText, js_clearClipboard: for clipboard
 BASE_LDFLAGS = -sALLOW_MEMORY_GROWTH -sERROR_ON_UNDEFINED_SYMBOLS=0 \
                -s "EXPORTED_RUNTIME_METHODS=['HEAPU8','HEAP8','HEAP32','ccall']" \
                -sASYNCIFY=1 \
                -sASYNCIFY_STACK_SIZE=8192 \
-               -sASYNCIFY_IMPORTS=['startModal']
+               -sASYNCIFY_IMPORTS=['startModal','js_writeTextToClipboard','js_readTextFromClipboard','js_clipboardHasText','js_clearClipboard']
 
 # GL-specific flags
 EM_GL_FLAGS = -sLEGACY_GL_EMULATION -sMAX_WEBGL_VERSION=2