fix(web): make the Emscripten build produce a module the browser will accept

Two independent blockers, both found running the web build against a current emsdk (5.0.7)
after the Game-lifetime crash in 16c3b67 was fixed:

- sol2 v3.3.0 does not compile. optional<T&>::emplace calls this->construct(), which that
  specialization does not have; because optional<T&> is a full specialization the lookup is
  not deferred, so a newer clang diagnoses it even though nothing instantiates it, and
  LuaScriptRunner.cpp fails. v3.3.1 still has it; v3.5.0 replaced the body with a placement-new
  that returns properly, so the pin moves there.

- The linked module was rejected by the browser at instantiation:
  "module uses a mix of legacy and new exception handling instructions". CNA selects the
  standardized try_table exception ABI (-sWASM_LEGACY_EXCEPTIONS=0) in its own root
  CMakeLists, while this project passed only -fwasm-exceptions -- so everything under CNA_dep
  used one ABI and MeshCraft's own objects, lua54, imgui, manifold and tinygltf used the
  other. Matching CNA's flag puts every object in the link on the same ABI.

Verified end to end in headless Chrome: the editor now loads and renders -- menu bar, toolbar,
hierarchy panel, viewport grid, Properties panel, "0 objects" status -- with "[MeshCraft] New
scene" in the output and not a single exception in the console, where the same page previously
died immediately after that line.

Author: robertvokac

CMakeLists.txt

@@ -106,8 +106,14 @@ meshcraft_select_graphics_backend(
     MESH_CRAFT_GRAPHICS_BACKEND_UPPER)
 
 if(EMSCRIPTEN)
-    add_compile_options(-fwasm-exceptions)
-    add_link_options(-fwasm-exceptions)
+    # -sWASM_LEGACY_EXCEPTIONS=0 must match CNA, which sets it in its own root CMakeLists: it
+    # selects the standardized try_table exception ABI over Emscripten's still-default legacy
+    # `try`. Without it, MeshCraft's own objects and its third-party subtrees (lua54, imgui,
+    # manifold, tinygltf) are built on the legacy ABI while everything under CNA_dep uses the
+    # standardized one, and the browser refuses the linked module outright:
+    # "module uses a mix of legacy and new exception handling instructions".
+    add_compile_options(-fwasm-exceptions -sWASM_LEGACY_EXCEPTIONS=0)
+    add_link_options(-fwasm-exceptions -sWASM_LEGACY_EXCEPTIONS=0)
 endif()
 
 if(NOT MESH_CRAFT_GRAPHICS_BACKEND_UPPER MATCHES "^(SDL_RENDERER|EASYGL|BGFX|VULKAN|WEBGPU)$")
@@ -415,9 +421,14 @@ else()
     target_compile_options(lua54 PRIVATE /w)
 endif()
 
+# v3.3.0 and v3.3.1 do not compile with a current clang: optional<T&>::emplace calls a
+# this->construct() that specialization does not have, and since optional<T&> is a full
+# specialization the lookup is not deferred, so newer clang reports it even though nothing
+# instantiates it. v3.5.0 replaced that body with a placement-new that returns properly.
+# Found when the Emscripten build (emsdk 5.0.7) stopped on LuaScriptRunner.cpp.
 FetchContent_Declare(sol2
     GIT_REPOSITORY https://github.com/ThePhD/sol2.git
-    GIT_TAG        v3.3.0
+    GIT_TAG        v3.5.0
     GIT_SHALLOW    TRUE
 )
 FetchContent_MakeAvailable(sol2)