WIP: TIN terrain system - 95% complete

Replaces heightfield with Cesium Quantized Mesh format (TIN).
Full replacement, not hybrid - TIN is the only terrain format.

Implemented:
- Format: quantizedmeshformat.h, quantizedmeshreader.h
- Triangulator: terraincooker_tin.{h,cpp} using CDT
- Cooker: terraincook now generates TIN by default
- Loader: terraintileloader fully rewritten for TIN
- GPU pool: terraintilepool_tin (VBO/IBO per tile)
- Renderer interface: terrainclipmap.cppm updated
- Shaders: terrainclipmap_tin.{vert,frag}
- Documentation: 5 comprehensive markdown files

Remaining:
- terrainclipmap.cpp render() method (partial, needs completion)
- Build testing and integration
- See TIN_INTEGRATION_GUIDE.md for next steps

Stats: 2700+ lines new code, ~50% vertex reduction expected

rendering/terraintileloader.cpp

@@ -15,7 +15,7 @@ module;
 #include <thread>
 #include <utility>
 #include <vector>
-#include "scene/heightfieldreader.h"
+#include "scene/quantizedmeshreader.h"
 
 module eu07.rendering.terraintileloader;
 
@@ -120,7 +120,36 @@ terrain_tile_loader::work() {
         // wish list while a tile is being decoded
         payload result;
         result.tile = tile;
-        result.valid = m_reader.read_level( tile.x, tile.z, tile.level, result.heights, result.materials );
+        
+        quantizedmesh::reader::tile_data data;
+        result.valid = m_reader.read_tile( tile.x, tile.z, tile.level, data );
+        
+        if( result.valid ) {
+            // Copy data to payload
+            result.positions_x = std::move( data.positions_x );
+            result.positions_y = std::move( data.positions_y );
+            result.positions_z = std::move( data.positions_z );
+            result.uvs_u = std::move( data.uvs_u );
+            result.uvs_v = std::move( data.uvs_v );
+            result.materials = std::move( data.materials );
+            result.indices = std::move( data.indices );
+            
+            result.north_edge = std::move( data.north_edge );
+            result.south_edge = std::move( data.south_edge );
+            result.west_edge = std::move( data.west_edge );
+            result.east_edge = std::move( data.east_edge );
+            
+            result.center_x = data.center_x;
+            result.center_y = data.center_y;
+            result.center_z = data.center_z;
+            result.min_x = data.min_x;
+            result.min_y = data.min_y;
+            result.min_z = data.min_z;
+            result.max_x = data.max_x;
+            result.max_y = data.max_y;
+            result.max_z = data.max_z;
+            result.geometric_error = data.geometric_error;
+        }
 
         std::lock_guard<std::mutex> lock( m_mutex );
         m_running.reset();