feat: rebuild Tutorial scene avec ProBuilder, matériaux gel/terrain

- Scène Tutorial reconstruite de zéro : sol ProBuilder 120x120, murs, rampes
- Zones race : 5 checkpoints (CP0→Finish) avec BoxCollider + CheckpointTrigger
- Gel pads : GelOrange (boost), GelBleu (bounce), GelViolet (sticky)
- Plateforme centrale pour mode teams (CaptureZone)
- Nouveaux matériaux URP : FloorMat, WallMat, CheckpointMat, GelOrangeMat, GelBleuMat, GelVioletMat, PlatformMat

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

game/.gitignore

@@ -0,0 +1,77 @@
+# =============== #
+# Unity generated  #
+# =============== #
+/[Ll]ibrary/
+/[Tt]emp/
+/[Oo]bj/
+/[Bb]uild/
+/[Bb]uilds/
+/[Ll]ogs/
+/[Uu]serSettings/
+/[Mm]emoryCaptures/
+/[Rr]ecordings/
+
+# ===================================== #
+# Visual Studio / Rider / IDE generated #
+# ===================================== #
+.vs/
+.vscode/
+*.csproj
+*.sln
+*.slnx
+*.suo
+*.tmp
+*.user
+*.userprefs
+*.pidb
+*.booproj
+*.svd
+*.pdb
+*.mdb
+*.opendb
+*.VC.db
+*.idea/
+
+# ============ #
+# OS generated #
+# ============ #
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+Desktop.ini
+
+# ======================== #
+# Unity build outputs      #
+# ======================== #
+/[Ww]eb[Gg][Ll] [Bb]uilds/
+/[Aa]ndroid/
+*.apk
+*.aab
+*.unitypackage
+*.app
+
+# ======================== #
+# Crashlytics / Autogenerated #
+# ======================== #
+crashlytics-build.properties
+sysinfo.txt
+
+# ======================== #
+# Asset meta recovery      #
+# ======================== #
+Assets/_Recovery/
+
+# ======================== #
+# Packaging                #
+# ======================== #
+*.unitypackage
+
+# ======================== #
+# Nuget                    #
+# ======================== #
+/[Nn]u[Gg]et/
+packages/