feat(solver): add kindred solver addon as submodule

Add mods/solver/ submodule pointing to kindred/solver.git which contains
the Phase 1 expression-based Newton-Raphson constraint solver implementing
the IKCSolver interface via kcsolve.register_solver().

Phase 1 supports: Coincident, DistancePointPoint, Fixed constraints.

Also adds CMake install rules for the solver addon.

.gitmodules

@@ -18,3 +18,7 @@
 	path = mods/silo
 	url = https://git.kindred-systems.com/kindred/silo-mod.git
 	branch = main
+[submodule "mods/solver"]
+	path = mods/solver
+	url = https://git.kindred-systems.com/kindred/solver.git
+	branch = main

src/Mod/Create/CMakeLists.txt

@@ -84,3 +84,18 @@ install(
     DESTINATION
         mods/sdk
 )
+
+# Install Kindred Solver addon
+install(
+    DIRECTORY
+        ${CMAKE_SOURCE_DIR}/mods/solver/kindred_solver
+    DESTINATION
+        mods/solver
+)
+install(
+    FILES
+        ${CMAKE_SOURCE_DIR}/mods/solver/package.xml
+        ${CMAKE_SOURCE_DIR}/mods/solver/Init.py
+    DESTINATION
+        mods/solver
+)