feat: desaturate quest markers for trivial (gray) quests

Trivial/low-level quests now show gray '!' / '?' markers instead of
yellow, matching the in-game distinction between available and trivial
quests. Add grayscale parameter to QuestMarkerRenderer::setMarker and
the push-constant block; application sets grayscale=1.0 for trivial
markers and 0.0 for all others.

assets/shaders/quest_marker.frag.glsl

@@ -5,6 +5,7 @@ layout(set = 1, binding = 0) uniform sampler2D markerTexture;
 layout(push_constant) uniform Push {
     mat4 model;
     float alpha;
+    float grayscale;  // 0 = full colour, 1 = fully desaturated (trivial quests)
 } push;
 
 layout(location = 0) in vec2 TexCoord;
@@ -14,5 +15,7 @@ layout(location = 0) out vec4 outColor;
 void main() {
     vec4 texColor = texture(markerTexture, TexCoord);
     if (texColor.a < 0.1) discard;
-    outColor = vec4(texColor.rgb, texColor.a * push.alpha);
+    float lum = dot(texColor.rgb, vec3(0.299, 0.587, 0.114));
+    vec3 rgb = mix(texColor.rgb, vec3(lum), push.grayscale);
+    outColor = vec4(rgb, texColor.a * push.alpha);
 }

include/rendering/quest_marker_renderer.hpp

@@ -35,8 +35,10 @@ public:
      * @param position World position (NPC base position)
      * @param markerType 0=available(!), 1=turnin(?), 2=incomplete(?)
      * @param boundingHeight NPC bounding height (optional, default 2.0f)
+     * @param grayscale 0 = full colour, 1 = desaturated grey (trivial/low-level quests)
      */
-    void setMarker(uint64_t guid, const glm::vec3& position, int markerType, float boundingHeight = 2.0f);
+    void setMarker(uint64_t guid, const glm::vec3& position, int markerType,
+                   float boundingHeight = 2.0f, float grayscale = 0.0f);
 
     /**
      * Remove a quest marker
@@ -61,6 +63,7 @@ private:
         glm::vec3 position;
         int type; // 0=available, 1=turnin, 2=incomplete
         float boundingHeight = 2.0f;
+        float grayscale = 0.0f; // 0 = colour, 1 = desaturated (trivial quests)
     };
 
     std::unordered_map<uint64_t, Marker> markers_;

src/rendering/quest_marker_renderer.cpp

@@ -17,8 +17,9 @@ namespace wowee { namespace rendering {
 
 // Push constant layout matching quest_marker.vert.glsl / quest_marker.frag.glsl
 struct QuestMarkerPushConstants {
-    glm::mat4 model;  // 64 bytes, used by vertex shader
+    glm::mat4 model;   // 64 bytes, used by vertex shader
-    float alpha;       // 4 bytes, used by fragment shader
+    float alpha;        // 4 bytes, used by fragment shader
+    float grayscale;    // 4 bytes: 0=colour, 1=desaturated (trivial quests)
 };
 
 QuestMarkerRenderer::QuestMarkerRenderer() {
@@ -340,8 +341,9 @@ void QuestMarkerRenderer::loadTextures(pipeline::AssetManager* assetManager) {
     }
 }
 
-void QuestMarkerRenderer::setMarker(uint64_t guid, const glm::vec3& position, int markerType, float boundingHeight) {
+void QuestMarkerRenderer::setMarker(uint64_t guid, const glm::vec3& position, int markerType,
-    markers_[guid] = {position, markerType, boundingHeight};
+                                    float boundingHeight, float grayscale) {
+    markers_[guid] = {position, markerType, boundingHeight, grayscale};
 }
 
 void QuestMarkerRenderer::removeMarker(uint64_t guid) {
@@ -436,10 +438,11 @@ void QuestMarkerRenderer::render(VkCommandBuffer cmd, VkDescriptorSet perFrameSe
         vkCmdBindDescriptorSets(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS, pipelineLayout_,
             1, 1, &texDescSets_[marker.type], 0, nullptr);
 
-        // Push constants: model matrix + alpha
+        // Push constants: model matrix + alpha + grayscale tint
         QuestMarkerPushConstants push{};
         push.model = model;
         push.alpha = fadeAlpha;
+        push.grayscale = marker.grayscale;
 
         vkCmdPushConstants(cmd, pipelineLayout_,
             VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT,