chore(renderer): refactor renderer and add post-process + spell visuals systems

- Updated core render pipeline and renderer integration in CMakeLists.txt, renderer.cpp, renderer.hpp
- Added post-process pipeline module:
  - post_process_pipeline.hpp
  - post_process_pipeline.cpp
- Added spell visual system module:
  - spell_visual_system.hpp
  - spell_visual_system.cpp
- Adjusted application/audio integration:
  - application.cpp
  - audio_coordinator.cpp

include/rendering/spell_visual_system.hpp

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <vector>
+#include <unordered_map>
+#include <unordered_set>
+#include <glm/glm.hpp>
+
+namespace wowee {
+namespace pipeline { class AssetManager; }
+namespace rendering {
+
+class M2Renderer;
+
+class SpellVisualSystem {
+public:
+    SpellVisualSystem() = default;
+    ~SpellVisualSystem() = default;
+
+    // Initialize with references to the M2 renderer (for model loading/instance spawning)
+    void initialize(M2Renderer* m2Renderer);
+    void shutdown();
+
+    // Spawn a spell visual at a world position.
+    // useImpactKit=false → CastKit path; useImpactKit=true → ImpactKit path
+    void playSpellVisual(uint32_t visualId, const glm::vec3& worldPosition,
+                         bool useImpactKit = false);
+
+    // Advance lifetime timers and remove expired instances.
+    void update(float deltaTime);
+
+    // Remove all active spell visual instances and reset caches.
+    // Called on map change / combat reset.
+    void reset();
+
+private:
+    // Spell visual effects — transient M2 instances spawned by SMSG_PLAY_SPELL_VISUAL/IMPACT
+    struct SpellVisualInstance {
+        uint32_t instanceId;
+        float elapsed;
+        float duration;  // per-instance lifetime in seconds (from M2 anim or default)
+    };
+
+    void loadSpellVisualDbc();
+
+    M2Renderer* m2Renderer_ = nullptr;
+    pipeline::AssetManager* cachedAssetManager_ = nullptr;
+
+    std::vector<SpellVisualInstance> activeSpellVisuals_;
+    std::unordered_map<uint32_t, std::string> spellVisualCastPath_;   // visualId → cast M2 path
+    std::unordered_map<uint32_t, std::string> spellVisualImpactPath_; // visualId → impact M2 path
+    std::unordered_map<std::string, uint32_t> spellVisualModelIds_;   // M2 path → M2Renderer modelId
+    std::unordered_set<uint32_t> spellVisualFailedModels_;           // modelIds that failed to load (negative cache)
+    uint32_t nextSpellVisualModelId_ = 999000; // Reserved range 999000-999799
+    bool spellVisualDbcLoaded_ = false;
+    static constexpr float SPELL_VISUAL_MAX_DURATION = 5.0f;
+    static constexpr float SPELL_VISUAL_DEFAULT_DURATION = 2.0f;
+};
+
+} // namespace rendering
+} // namespace wowee