fix(build): fix remaining ImageMap merge type conflicts

- ExtrusionEntityCollection: first/last_point() must return const Point&
  to match the virtual signature in ExtrusionEntity base class
- AppConfig: remove ImageMap-specific VERSION_CHECK_URL_LEGACY,
  VERSION_CHECK_MODE, VERSION_DOWNLOAD_URL constants; simplify methods
  to use our single Gitea URL
- ExtrusionProcessor: restore dimension-bridging in maybe_unscale lambda
  so 2D polyline points work with the 3D (Linef3) boundary distancer
  used in the ZAA overhang slowdown path

src/libslic3r/AppConfig.cpp

@@ -1607,24 +1607,17 @@ std::string AppConfig::version_check_url() const
     auto from_settings = get("version_check_url");
     if (!from_settings.empty())
         return from_settings;
-
-    auto mode = version_check_mode();
-    boost::algorithm::to_lower(mode);
-    if (mode == "platform_json" || mode == "json_platform")
-        return VERSION_CHECK_URL;
-    return VERSION_CHECK_URL_LEGACY;
+    return VERSION_CHECK_URL;
 }
 
 std::string AppConfig::version_check_mode() const
 {
-    auto from_settings = get("version_check_mode");
-    return from_settings.empty() ? VERSION_CHECK_MODE : from_settings;
+    return get("version_check_mode");
 }
 
 std::string AppConfig::version_download_url() const
 {
-    auto from_settings = get("version_download_url");
-    return from_settings.empty() ? VERSION_DOWNLOAD_URL : from_settings;
+    return get("version_download_url");
 }
 
 std::string AppConfig::profile_update_url() const

src/libslic3r/ExtrusionEntityCollection.hpp

@@ -157,8 +157,8 @@ public:
     ExtrusionEntityCollection chained_path_from(const Point &start_near, ExtrusionRole role = erMixed) const 
     	{ return this->no_sort ? *this : chained_path_from(this->entities, start_near, role); }
     void reverse() override;
-    Point first_point() const override { return this->entities.front()->first_point(); }
-    Point last_point() const override { return this->entities.back()->last_point(); }
+    const Point& first_point() const override { return this->entities.front()->first_point(); }
+    const Point& last_point() const override { return this->entities.back()->last_point(); }
 
     // Produce a list of 2D polygons covered by the extruded paths, offsetted by the extrusion width.
     // Increase the offset by scaled_epsilon to achieve an overlap, so a union will produce no gaps.

src/libslic3r/GCode/ExtrusionProcessor.hpp

@@ -82,7 +82,19 @@ std::vector<ExtendedPoint<L::Dim>> estimate_points_properties(const POINTS&
     if (input_points.empty())
         return {};
     float boundary_offset = PREV_LAYER_BOUNDARY_OFFSET ? 0.5 * flow_width : 0.0f;
-    auto  maybe_unscale   = [](const P& p) -> Vec { return SCALED_INPUT ? unscaled(p) : p.template cast<double>(); };
+    auto  maybe_unscale   = [](const P& p) -> Vec {
+        if constexpr (P::RowsAtCompileTime == 3 && L::Dim == 2) {
+            // 3D input point but 2D distancer — project to XY
+            return SCALED_INPUT ? unscaled(p).template head<2>() : p.template head<2>().template cast<double>();
+        } else if constexpr (P::RowsAtCompileTime == 2 && L::Dim == 3) {
+            // 2D input point but 3D distancer — embed in XY plane (z=0)
+            Vec v = Vec::Zero();
+            v.template head<2>() = SCALED_INPUT ? unscaled(p) : p.template cast<double>();
+            return v;
+        } else {
+            return SCALED_INPUT ? unscaled(p) : p.template cast<double>();
+        }
+    };
 
     std::vector<ExtendedPoint<L::Dim>> points;
     points.reserve(input_points.size() * (ADD_INTERSECTIONS ? 1.5 : 1));