fix: resolve 7 code quality issues across PRs #59-63

- Remove stale kVOffset (-0.15) from zone_highlight_layer hover detection;
  the offset was removed from rendering but left in the hit-test path,
  shifting hover ~15% vertically
- Add null guard for cachedGameHandler_ in ChatPanel::inputTextCallback
  to prevent dereference before first render frame
- Zero WindowBorderSize in world map ImGui window to eliminate gap
  between window edge and map content
- Replace hardcoded cosmic highlight multipliers with displayH×displayH
  square rendering, preserving 1:1 aspect ratio at any resolution
- Skip transport waypoints where serverToCanonical zeroes nonzero input
  instead of silently building paths with broken (0,0,0) coordinates
- Use length-squared check (posLenSq > 1.0) for spline endpoint
  validation instead of per-component != 0 comparison, so entities
  near the world origin are no longer skipped
- Fix off-by-one in ChatPanel::insertChatLink buffer capacity check

src/rendering/world_map/layers/zone_highlight_layer.cpp

@@ -172,10 +172,6 @@ void ZoneHighlightLayer::render(const LayerContext& ctx) {
         float mv = (mousePos.y - ctx.imgMin.y) / ctx.displayH;
 
         if (mu >= 0.0f && mu <= 1.0f && mv >= 0.0f && mv <= 1.0f) {
-            // Undo the -0.15 vertical offset applied during continent rendering
-            constexpr float kVOffset = -0.15f;
-            mv -= kVOffset;
-
             // Screen UV → world coordinates
             float wowX = cLeft - mu * cDenomU;
             float wowY = cTop  - mv * cDenomV;

src/rendering/world_map/world_map_facade.cpp

@@ -590,6 +590,7 @@ void WorldMapFacade::Impl::renderImGuiOverlay(const glm::vec3& playerRenderPos,
 
     ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0, 0));
     ImGui::PushStyleVar(ImGuiStyleVar_ItemSpacing, ImVec2(0, 0));
+    ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
 
     // Bug fix: pass nullptr instead of &open so ImGui's X-button doesn't
     // set open=false directly — that bypasses cleanup (userMapOverride,
@@ -979,19 +980,17 @@ void WorldMapFacade::Impl::renderImGuiOverlay(const glm::vec3& playerRenderPos,
                     //   • Full stretch (like WoW original): hlW = displayW, hlH = displayH
                     //   • Shift glow position: adjust hlX offset
                     //
-                    float hlW,hlH,hlX, hlY;
+                    // Render highlight as a square (side = displayH) to preserve
+                    // the 1:1 aspect of the 512×512 glow textures at any resolution.
+                    float hlW = displayH;
+                    float hlH = displayH;
+                    float hlX, hlY;
                     if (cosmicLabel == "azeroth") {
-                        hlW = displayW * 0.90f;            // width  of highlight rect (= square)
-                        hlH = displayH * 0.985f;           // height of highlight rect (= square)
-                    
-                        hlX = imgMax.x - hlW;              // flush right
-                        hlY = imgMax.y - hlH;              // flush bottom + title bar
+                        hlX = imgMax.x - hlW;   // flush right (glow sits in right-center of texture)
+                        hlY = imgMin.y;          // flush top
                     } else {
-                        hlW = displayW * 0.86f;            // width  of highlight rect (= square)
-                        hlH = displayH * 0.91f;            // height of highlight rect (= square)
-                        
-                        hlX = imgMin.x + displayW * 0.02f; // flush left
-                        hlY = imgMax.y - displayH * 0.95f; // flush bottom
+                        hlX = imgMin.x;          // flush left (glow sits in left-center of texture)
+                        hlY = imgMin.y;          // flush top
                     }
 
                     if (zoneHighlightLayer) {
@@ -1064,7 +1063,7 @@ void WorldMapFacade::Impl::renderImGuiOverlay(const glm::vec3& playerRenderPos,
     }
     ImGui::End();
 
-    ImGui::PopStyleVar(2);  // WindowPadding + ItemSpacing
+    ImGui::PopStyleVar(3);  // WindowPadding + ItemSpacing + WindowBorderSize
 }
 
 } // namespace world_map