Update documentation to use ModelingToolkit's enhanced problem constructor docstrings

Modified docs/src/API/problems.md to reference ModelingToolkit's exported problem
constructors directly instead of always using SciMLBase references. This ensures
that the generated documentation shows ModelingToolkit's enhanced docstrings that
include references to both MTK's problem building documentation and the relevant
solver documentation.

Updated references:
- ODEProblem, SDEProblem, JumpProblem → Now use MTK's enhanced docstrings
- NonlinearProblem, OptimizationProblem, SteadyStateProblem → Now use MTK's enhanced docstrings
- IntervalNonlinearProblem, DiscreteProblem, ImplicitDiscreteProblem → Now use MTK's enhanced docstrings

Non-exported types (DAEProblem, DDEProblem, BVProblem, LinearProblem) still reference
SciMLBase versions, but users calling these through ModelingToolkit will see the
enhanced docstrings in the REPL help system.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: claude

docs/src/API/problems.md

@@ -14,31 +14,31 @@ code for a variety of such numerical problems.
 
 ```@docs
 SciMLBase.ODEFunction
-SciMLBase.ODEProblem
+ODEProblem
 SciMLBase.DAEFunction
 SciMLBase.DAEProblem
 SciMLBase.SDEFunction
-SciMLBase.SDEProblem
+SDEProblem
 SciMLBase.DDEFunction
 SciMLBase.DDEProblem
 SciMLBase.SDDEFunction
 SciMLBase.SDDEProblem
-JumpProcesses.JumpProblem
+JumpProblem
 SciMLBase.BVProblem
-SciMLBase.DiscreteProblem
-SciMLBase.ImplicitDiscreteProblem
+DiscreteProblem
+ImplicitDiscreteProblem
 ```
 
 ## Linear and Nonlinear systems
 
 ```@docs
 SciMLBase.NonlinearFunction
-SciMLBase.NonlinearProblem
+NonlinearProblem
 SciMLBase.SCCNonlinearProblem
 SciMLBase.NonlinearLeastSquaresProblem
-SciMLBase.SteadyStateProblem
+SteadyStateProblem
 SciMLBase.IntervalNonlinearFunction
-SciMLBase.IntervalNonlinearProblem
+IntervalNonlinearProblem
 ModelingToolkit.HomotopyContinuationProblem
 SciMLBase.HomotopyNonlinearFunction
 SciMLBase.LinearProblem
@@ -48,7 +48,7 @@ SciMLBase.LinearProblem
 
 ```@docs
 SciMLBase.OptimizationFunction
-SciMLBase.OptimizationProblem
+OptimizationProblem
 SciMLBase.ODEInputFunction
 ModelingToolkit.JuMPDynamicOptProblem
 ModelingToolkit.InfiniteOptDynamicOptProblem