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>

include/rendering/character_renderer.hpp

@@ -49,7 +49,7 @@ public:
     CharacterRenderer();
     ~CharacterRenderer();
 
-    bool initialize(VkContext* ctx, VkDescriptorSetLayout perFrameLayout, pipeline::AssetManager* am,
+    [[nodiscard]] bool initialize(VkContext* ctx, VkDescriptorSetLayout perFrameLayout, pipeline::AssetManager* am,
                     VkRenderPass renderPassOverride = VK_NULL_HANDLE,
                     VkSampleCountFlagBits msaaSamples = VK_SAMPLE_COUNT_1_BIT);
     void shutdown();
@@ -71,7 +71,7 @@ public:
     void prepareRender(uint32_t frameIndex);
     void render(VkCommandBuffer cmd, VkDescriptorSet perFrameSet, const Camera& camera);
     void recreatePipelines();
-    bool initializeShadow(VkRenderPass shadowRenderPass);
+    [[nodiscard]] bool initializeShadow(VkRenderPass shadowRenderPass);
     void renderShadow(VkCommandBuffer cmd, const glm::mat4& lightSpaceMatrix,
                       const glm::vec3& shadowCenter = glm::vec3(0), float shadowRadius = 1e9f);