Keep editor alive when game code throws an exception

[mblackman]

Problem

The editor runs the project in-process (editor mode is the same Game instance with isPaused-gated systems). An uncaught exception from game or Lua code propagated up through FrameLoop → Game::Run's loop and crashed the whole editor. (The separate Run Player button already isolates crashes via a child process — that path was never affected.)

Change

New header-only RunEditorGuarded(GameConfig&, context, fn) in src/Engine/EditorExceptionGuard.h:

• In editor mode: catches std::exception (and ...), logs it via Logger::Error (surfaces in the editor Console panel), and sets isPaused = true — so the editor stays alive and the throwing tick doesn't re-raise every frame. Fix the script, hit Play again.
• Outside editor mode (standalone player, headless bench/bake/CI): passthrough — exceptions propagate unchanged, no try/catch overhead beyond one bool check.

Applied at the three seams where game code executes during an editor session:

1. FrameLoop::Update — the per-frame tick (registry_->Update), which runs every system including Lua.
2. FrameLoop::ProcessInput — the key/mouse/wheel EmitEvent dispatches (Lua input handlers, UIButtonSystem callbacks).
3. EditorToolbarPanel Play/Stop — ReloadScene/StopScene, which run during ImGui render outside the Update guard. A broken scene load on Play was a real editor-crash path; Play now only un-pauses if the reload succeeded.

Lua runtime errors inside a script's update were already swallowed by ScriptSystem's protected_function. This covers the harder failures: C++ exceptions from systems/bindings, and scene loads / input callbacks invoked outside a protected boundary.

Verification

• cmake --build build/editor-debug — clean.
• clang-format 18.1.8 — passes on all three files.