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.Dynamic.sine.Uniform.tcl.txt

@@ -0,0 +1,78 @@
+# --------------------------------------------------------------------------------------------------
+# Example4. 2D Portal Frame--  Dynamic sine-wave input analysis
+#                                 Silvia Mazzoni, 2006
+# execute this file after you have built the model, and after you apply gravity
+#
+
+# Uniform Sine-Wave ground motion (uniform acceleration input at all support nodes)
+set GMdirection 1;			# ground-motion direction
+set GMSineAccAmpl [expr 0.5*$g];	# sine ground-motion acceleration amplitude (this is the support motion, not the free-node motion)
+set TPeriodSine [expr 0.35*$sec];	# period of input sine wave
+set DurationSine [expr 3.*$sec];	# duration of input sine wave
+
+# set up ground-motion-analysis parameters
+set DtAnalysis	[expr 0.01*$sec];	# time-step Dt for lateral analysis
+set TmaxAnalysis	[expr 10. *$sec];	# maximum duration of ground-motion analysis -- should be 50*$sec
+
+# ----------- set up analysis parameters
+source LibAnalysisDynamicParameters.tcl;	# constraintsHandler,DOFnumberer,system-ofequations,convergenceTest,solutionAlgorithm,integrator
+
+# define DAMPING--------------------------------------------------------------------------------------
+# apply Rayleigh DAMPING from $xDamp
+# D=$alphaM*M + $betaKcurr*Kcurrent + $betaKcomm*KlastCommit + $beatKinit*$Kinitial
+set xDamp 0.02;				# 2% damping ratio
+set lambda [eigen 1]; 			# eigenvalue mode 1
+set omega [expr pow($lambda,0.5)];
+set alphaM 0.;				# M-prop. damping; D = alphaM*M
+set betaKcurr 0.;         			# K-proportional damping;      +beatKcurr*KCurrent
+set betaKcomm [expr 2.*$xDamp/($omega)];   	# K-prop. damping parameter;   +betaKcomm*KlastCommitt
+set betaKinit 0.;         			# initial-stiffness proportional damping      +beatKinit*Kini
+rayleigh $alphaM $betaKcurr $betaKinit $betaKcomm; 				# RAYLEIGH damping
+
+#  ---------------------------------    perform Dynamic Ground-Motion Analysis
+# the following commands are unique to the Sine-Wave excitation
+set IDloadTag 400;	# for uniformSupport excitation
+set DtGround [expr 0.005*$sec];	# time-step Dt for input grond motion
+set omegaSine [expr 2*$PI/$TPeriodSine];
+set vel0 [expr $GMSineAccAmpl*(-1)/$omegaSine];
+set AccelSeries "Sine 0. $DurationSine  $TPeriodSine -factor $GMSineAccAmpl "
+pattern UniformExcitation  $IDloadTag  $GMdirection  -accel $AccelSeries  -vel0 $vel0
+
+set Nsteps [expr int($TmaxAnalysis/$DtAnalysis)];
+set ok [analyze $Nsteps $DtAnalysis];			# actually perform analysis; returns ok=0 if analysis was successful
+
+if {$ok != 0} {      ;					# analysis was not successful.
+	# --------------------------------------------------------------------------------------------------
+	# change some analysis parameters to achieve convergence
+	# performance is slower inside this loop
+	#    Time-controlled analysis
+	set ok 0;
+	set controlTime [getTime];
+	while {$controlTime < $TmaxAnalysis && $ok == 0} {
+		set controlTime [getTime]
+		set ok [analyze 1 $DtAnalysis]
+		if {$ok != 0} {
+			puts "Trying Newton with Initial Tangent .."
+			test NormDispIncr   $Tol 1000  0
+			algorithm Newton -initial
+			set ok [analyze 1 $DtAnalysis]
+			test $testTypeDynamic $TolDynamic $maxNumIterDynamic  0
+			algorithm $algorithmTypeDynamic
+		}
+		if {$ok != 0} {
+			puts "Trying Broyden .."
+			algorithm Broyden 8
+			set ok [analyze 1 $DtAnalysis]
+			algorithm $algorithmTypeDynamic
+		}
+		if {$ok != 0} {
+			puts "Trying NewtonWithLineSearch .."
+			algorithm NewtonLineSearch .8
+			set ok [analyze 1 $DtAnalysis]
+			algorithm $algorithmTypeDynamic
+		}
+	}
+};      # end if ok !0
+
+
+puts "Ground Motion Done. End Time: [getTime]"