ifcviewer: preset-driven nav mouse bindings + a "Web" preset (desktop + web)

Make orbit/pan/select mouse bindings pure data owned by ViewportCore so both
hosts and every preset share one source of truth, and add a "Web" preset. This
rounds out the matrix: the desktop gains a web-style scheme and the web inherits
all presets, with no per-platform hardcoding.

- Core: NavBindings { orbit, pan, select button + modifier } + setNavPreset
  ("blender" default | "rhino" | "revit" | "web") + navBindings(). Select is
  preset-driven too (was hardcoded LMB) so "web" moves it to RMB. web = orbit
  LMB, pan MMB, select RMB (LMB drag orbits with no click/drag ambiguity; RMB
  click-selects / drag-marquees). NavMod uses "Plain" not "None" (X11 #defines
  None to 0L).
- Desktop ViewportWindow: applyNavPreset sources the core table (mapped to Qt);
  marquee-arm / single-pick dispatch keys off select_button_. Default stays
  blender → no behaviour change.
- Desktop config: AppSettings::NavPreset gains Web + navPresetName(); the
  Settings dialog lists it. This also FIXES a pre-existing gap — the preset combo
  was persisted but never applied (only WGPU_NAV_PRESET env worked). MainWindow
  now applies the persisted preset at startup (env override still wins) and live
  on navPresetChanged, so all four presets actually work from the dialog.
- Web main_web: classifyPress routes the pressed button through navBindings()
  (orbit/pan/select), defaulting to the "web" preset; context menu already
  suppressed so RMB is free.

Tests: setNavPreset table (Catch2, 123 total); web smoke select tests use RMB.
BonsaiViewer builds; 9/9 web smoke.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ifcviewer/AppSettings.h

@@ -37,13 +37,18 @@ public:
     //   Blender   — Orbit MMB,        Pan Shift+MMB   (current default)
     //   Rhino     — Orbit RMB,        Pan Shift+RMB
     //   Revit     — Orbit Shift+MMB,  Pan MMB
+    //   Web       — Orbit LMB,        Pan MMB,        Select RMB
     enum class NavPreset {
         Blender = 0,
         Rhino   = 1,
         Revit   = 2,
+        Web     = 3,
     };
     Q_ENUM(NavPreset)
 
+    // Preset → the lowercase name ViewportCore::setNavPreset / applyNavPreset take.
+    static const char* navPresetName(NavPreset preset);
+
     static AppSettings& instance();
 
     QString geometryLibrary() const;