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/render_constants.hpp

@@ -0,0 +1,74 @@
+#pragma once
+
+#include <cstdint>
+
+// Rendering-domain constants: distances, LOD thresholds, particle tuning.
+
+namespace wowee {
+namespace rendering {
+
+// ---------------------------------------------------------------------------
+// M2 instance-count → render-distance mapping
+// ---------------------------------------------------------------------------
+constexpr uint32_t M2_HIGH_DENSITY_INSTANCE_THRESHOLD = 2000;
+constexpr float    M2_MAX_RENDER_DISTANCE_HIGH_DENSITY = 800.0f;
+constexpr float    M2_MAX_RENDER_DISTANCE_LOW_DENSITY  = 2800.0f;
+
+// ---------------------------------------------------------------------------
+// M2 LOD / bone-update distance thresholds (world units)
+// ---------------------------------------------------------------------------
+constexpr float M2_LOD3_DISTANCE        = 150.0f;  // Beyond this: no bone updates
+constexpr float M2_BONE_SKIP_DIST_FAR   = 100.0f;  // Beyond this: every 4th frame
+constexpr float M2_BONE_SKIP_DIST_MID   = 50.0f;   // Beyond this: every 2nd frame
+
+// ---------------------------------------------------------------------------
+// M2 culling geometry
+// ---------------------------------------------------------------------------
+constexpr float M2_CULL_RADIUS_SCALE_DIVISOR = 12.0f;
+constexpr float M2_PADDED_RADIUS_SCALE       = 1.5f;
+constexpr float M2_PADDED_RADIUS_MIN_MARGIN  = 3.0f;
+
+// ---------------------------------------------------------------------------
+// M2 variation / idle animation timing (milliseconds)
+// ---------------------------------------------------------------------------
+constexpr float M2_VARIATION_TIMER_MIN_MS      = 3000.0f;
+constexpr float M2_VARIATION_TIMER_MAX_MS      = 11000.0f;
+constexpr float M2_LOOP_VARIATION_TIMER_MIN_MS = 4000.0f;
+constexpr float M2_LOOP_VARIATION_TIMER_MAX_MS = 10000.0f;
+constexpr float M2_IDLE_VARIATION_TIMER_MIN_MS = 2000.0f;
+constexpr float M2_IDLE_VARIATION_TIMER_MAX_MS = 6000.0f;
+constexpr float M2_DEFAULT_PARTICLE_ANIM_MS    = 3333.0f;
+
+// ---------------------------------------------------------------------------
+// HiZ occlusion culling
+// ---------------------------------------------------------------------------
+// VP matrix diff threshold — below this HiZ is considered safe.
+// Typical tracking camera (following a walking character) produces 0.05–0.25.
+constexpr float HIZ_VP_DIFF_THRESHOLD = 0.5f;
+
+// ---------------------------------------------------------------------------
+// Smoke / spark particle tuning
+// ---------------------------------------------------------------------------
+constexpr float SMOKE_OFFSET_XY_MIN  = -0.4f;
+constexpr float SMOKE_OFFSET_XY_MAX  =  0.4f;
+constexpr float SMOKE_VEL_Z_MIN      =  3.0f;
+constexpr float SMOKE_VEL_Z_MAX      =  5.0f;
+constexpr float SMOKE_LIFETIME_MIN   =  4.0f;
+constexpr float SMOKE_LIFETIME_MAX   =  7.0f;
+constexpr float SMOKE_Z_VEL_DAMPING  =  0.98f;
+constexpr float SMOKE_SIZE_START     =  1.0f;
+constexpr float SMOKE_SIZE_GROWTH    =  2.5f;
+
+constexpr int   SPARK_PROBABILITY_DENOM = 8;      // 1-in-8 chance per frame
+constexpr float SPARK_LIFE_BASE         = 0.8f;
+constexpr float SPARK_LIFE_RANGE        = 1.2f;
+
+// ---------------------------------------------------------------------------
+// Character rendering
+// ---------------------------------------------------------------------------
+// Default frustum-cull radius when model bounds are unavailable (world units).
+// 4.0 covers Tauren, mounted characters, and most creature models.
+constexpr float DEFAULT_CHARACTER_CULL_RADIUS = 4.0f;
+
+} // namespace rendering
+} // namespace wowee