feat: named case-result load combinations with full GUI support

Snapshots the current development tree, headlined by proper load
combinations (user request): a reusable LoadCombination entity of
weighted completed static-case results (e.g. 1.2xDead + 1.6xLive).

- core: LoadCombination/LoadCombinationItem entities, Project
  integration (lookup, unique ids, reference validation)
- services: combinations.py (linear superposition + envelope),
  exported via services __init__
- commands: undoable Add/Delete/Update for combinations
- GUI: Load Combinations manager dialog, Run-dialog evaluation,
  envelope display in Results panel, Combinations tab in Table dock
- tests: unit coverage (validation, math, error paths) + integration
  superposition check vs a single factored run

examples/data/Ex4.Portal2D.analyze.Static.Push.tcl.txt

@@ -0,0 +1,69 @@
+# --------------------------------------------------------------------------------------------------
+# Example4. 2D Portal Frame--  Static Pushover Analysis
+#                            Silvia Mazzoni & Frank McKenna, 2006
+# execute this file after you have built the model, and after you apply gravity
+#
+
+# we need to set up parameters that are particular to the model.
+set IDctrlNode 3;			# node where displacement is read for displacement control
+set IDctrlDOF 1;			# degree of freedom of displacement read for displacement contro
+# characteristics of pushover analysis
+set Dmax [expr 0.1*$LCol];		# maximum displacement of pushover. push to 10% drift.
+set Dincr [expr 0.001*$LCol];		# displacement increment for pushover. you want this to be very small, but not too small to slow down the analysis
+
+# create load pattern for lateral pushover load
+set Hload [expr $Weight/2];			# define the lateral load as a proportion of the weight so that the pseudo time equals the lateral-load coefficient when using linear load pattern
+set iPushNode "3 4";			# define nodes where lateral load is applied in static lateral analysis
+pattern Plain 200 Linear {;			# define load pattern -- generalized
+	foreach PushNode $iPushNode {
+		load $PushNode $Hload 0.0 0.0 0.0 0.0 0.0
+	}
+}
+
+# ----------- set up analysis parameters
+source LibAnalysisStaticParameters.tcl;	# constraintsHandler,DOFnumberer,system-ofequations,convergenceTest,solutionAlgorithm,integrator
+
+#  ---------------------------------    perform Static Pushover Analysis
+set Nsteps [expr int($Dmax/$Dincr)];        # number of pushover analysis steps
+set ok [analyze $Nsteps];                # this will return zero if no convergence problems were encountered
+set fmt1 "%s Pushover analysis: CtrlNode %.3i, dof %.1i, Disp=%.4f %s";	# format for screen/file output of DONE/PROBLEM analysis
+if {$ok != 0} {  
+	# if analysis fails, we try some other stuff, performance is slower inside this loop
+	set Dstep 0.0;
+	set ok 0
+	while {$Dstep <= 1.0 && $ok == 0} {	
+		set controlDisp [nodeDisp $IDctrlNode $IDctrlDOF ]
+		set Dstep [expr $controlDisp/$Dmax]
+		set ok [analyze 1 ]
+		# if analysis fails, we try some other stuff
+		# performance is slower inside this loop	global maxNumIterStatic;	    # max no. of iterations performed before "failure to converge" is ret'd
+		if {$ok != 0} {
+			puts "Trying Newton with Initial Tangent .."
+			test NormDispIncr   $Tol 2000 0
+			algorithm Newton -initial
+			set ok [analyze 1]
+			test $testTypeStatic $TolStatic      $maxNumIterStatic    0
+			algorithm $algorithmTypeStatic
+		}
+		if {$ok != 0} {
+			puts "Trying Broyden .."
+			algorithm Broyden 8
+			set ok [analyze 1 ]
+			algorithm $algorithmTypeStatic
+		}
+		if {$ok != 0} {
+			puts "Trying NewtonWithLineSearch .."
+			algorithm NewtonLineSearch 0.8 
+			set ok [analyze 1]
+			algorithm $algorithmTypeStatic
+		}
+
+	};	# end while loop
+};      # end if ok !0
+
+# -----------------------------------------------------------------------------------------------------
+if {$ok != 0 } {
+	puts [format $fmt1 "PROBLEM" $IDctrlNode $IDctrlDOF [nodeDisp $IDctrlNode $IDctrlDOF] $LunitTXT]
+} else {
+	puts [format $fmt1 "DONE"  $IDctrlNode $IDctrlDOF [nodeDisp $IDctrlNode $IDctrlDOF] $LunitTXT]
+}