[ALICE3] Updated ALICE 3 IRIS coldplate in O2 geometry (#15198)

* Updated ALICE 3 IRIS coldplate in O2 geometry

* Please consider the following formatting changes

---------

Co-authored-by: fcolamar <fabio.colamaria@cern.ch>
Co-authored-by: ALICE Action Bot <alibuild@cern.ch>

Author: 3 people

Detectors/Upgrades/ALICE3/TRK/simulation/src/TRKServices.cxx

@@ -108,7 +108,7 @@ void TRKServices::createMaterials()
   matmgr.Material("ALICE3_TRKSERVICES", 73, "BERYLLIUM", 9.01, 4., 1.848, 35.3, 36.7);                                                 // Beryllium - Candidate for IRIS vacuum vessel
   matmgr.Mixture("ALICE3_TRKSERVICES", 74, "ALUMINIUM5083", aAl5083, zAl5083, dAl5083, 9, wAl5083);                                    // AL5083 - Candidate for IRIS vacuum vessel
   matmgr.Mixture("ALICE3_TRKSERVICES", 75, "ALUMINIUMBERYLLIUMMETAL", aAlBeMet, zAlBeMet, dAlBeMet, 2, wAlBeMet);                      // Aluminium-Beryllium metal - Candidate for IRIS vacuum vessel
-  matmgr.Material("ALICE3_TRKSERVICES", 76, "CARBONFIBERM55J6K", 12.0107, 6, 1.92, 999, 999);                                          // Carbon Fiber M55J
+  matmgr.Material("ALICE3_TRKSERVICES", 76, "CARBONFIBERM55J6K", 12.0107, 6, 1.92, 22.4, 999);                                         // Carbon Fiber M55J
   matmgr.Mixture("ALICE3_PIPE", 77, "VACUUM", aAir, zAir, dAir1, 4, wAir);
 
   matmgr.Medium("ALICE3_TRKSERVICES", 1, "CERAMIC", 66, 0, ifield, fieldm, tmaxfd, stemax, deemax, epsil, stmin);                  // Ceramic for cold plate

Detectors/Upgrades/ALICE3/TRK/simulation/src/VDGeometryBuilder.cxx

@@ -272,8 +272,8 @@ static constexpr double kInclinedWallPhi0_deg = 27.799f;
 static constexpr double kInclinedWallRmax_cm = 4.75f; // 47.5 mm outer extension
 
 // Coldplate specs (cm)
-static constexpr double kColdplateRadius_cm = 2.6f;     // 26 mm (outer radius)
-static constexpr double kColdplateThickness_cm = 0.15f; // 1.5 mm
+static constexpr double kColdplateRadius_cm = 2.6f;     // 26 mm (inner radius)
+static constexpr double kColdplateThickness_cm = 0.02f; // 1.5 mm
 static constexpr double kColdplateZ_cm = 50.0f;         // full length
 
 // ========== φ-span helpers (gap/arc → degrees) ==========