fix(render): code quality cleanup

Magic number elimination:
- Create protocol_constants.hpp, warden_constants.hpp,
  render_constants.hpp, ui_constants.hpp
- Replace ~55 magic numbers across game_handler, warden_handler,
  m2_renderer_render

Reduce nesting depth:
- Extract 5 parseEffect* methods from handleSpellLogExecute
  (max indent 52 → 16 cols)
- Extract resolveSpellSchool/playSpellCastSound/playSpellImpactSound
  from 3× duplicate audio blocks in handleSpellGo
- Flatten SMSG_INVENTORY_CHANGE_FAILURE with early-return guards
- Extract drawScreenEdgeVignette() for 3 duplicate vignette blocks

DRY extract patterns:
- Replace 12 compound expansion checks with isPreWotlk() across
  movement_handler (9), chat_handler (1), social_handler (1)

const to constexpr:
- Promote 23+ static const arrays/scalars to static constexpr across
  12 source files

Error handling:
- Convert PIN auth from exceptions to std::optional<PinProof>
- Add [[nodiscard]] to 15+ initialize/parse methods
- Wrap ~20 unchecked initialize() calls with LOG_WARNING/LOG_ERROR

Signed-off-by: Pavel Okhlopkov <pavel.okhlopkov@flant.com>

src/rendering/terrain_manager.cpp

@@ -868,7 +868,8 @@ bool TerrainManager::advanceFinalization(FinalizingTile& ft) {
 
         // Ensure M2 renderer has asset manager
         if (m2Renderer && assetManager) {
-            m2Renderer->initialize(nullptr, VK_NULL_HANDLE, assetManager);
+            if (!m2Renderer->initialize(nullptr, VK_NULL_HANDLE, assetManager))
+                LOG_WARNING("M2Renderer terrain re-init failed");
         }
 
         ft.phase = FinalizationPhase::M2_MODELS;
@@ -952,7 +953,8 @@ bool TerrainManager::advanceFinalization(FinalizingTile& ft) {
     case FinalizationPhase::WMO_MODELS: {
         // Upload multiple WMO models per call (batched GPU uploads)
         if (wmoRenderer && assetManager) {
-            wmoRenderer->initialize(nullptr, VK_NULL_HANDLE, assetManager);
+            if (!wmoRenderer->initialize(nullptr, VK_NULL_HANDLE, assetManager))
+                LOG_WARNING("WMORenderer terrain re-init failed");
             // Set pre-decoded BLP cache and defer normal maps during streaming
             wmoRenderer->setPredecodedBLPCache(&pending->preloadedWMOTextures);
             wmoRenderer->setDeferNormalMaps(true);