Forward rigid connectors to quasi-static mechanics

[allamaprabhuani]

Summary

Correct boundary-condition dispatch for the staggered quasi_static route by
forwarding active rotation-free rigid connectors to QuasiStaticSolver.solve.
The solver already accepts this argument and implements reduced mechanics.
The explicit and legacy staggered routes already forward their connectors.

The previous call supplied the master Dirichlet values but omitted the slave
constraints. A six-node, four-element elastic regression detects the omission.
The corrected call recovers the connector-constrained solution and preserves
ordinary non-connector mechanics and the existing nonconvergence guard.

The contribution lane is solver boundary-condition dispatch. The implementation
was checked against BoundaryConditions, QuasiStaticSolver.solve, the
staggered dispatcher and the holed-plate configuration. Capability documentation
and the changelog describe the narrow validation scope.

Verification

• The new tests give five failures and one pass on the previous dispatcher,
  then all six pass with the argument forwarded.
• The full local suite passes 292 tests.
• CPU float64 isotropic elastic checks cover connector translation and rotation,
  an analytical reaction, moment balance, direct-solver agreement and the
  unchanged non-connector route.
• python -m pytest -q tests
• python -m phast run examples/quasistatic/notched_holed_plate/config.yaml --validate-only
• sphinx-build -W -b html docs <external-output-directory>
• git diff --check

On the old dispatcher, the small elastic case produces a maximum slave
displacement difference of 0.004 against the connector-constrained solution
under a prescribed master displacement of 0.01. This is a bounded regression,
not a newly executed full fracture benchmark.

Scope

The holed-plate example remains on quasi_static_legacy. Damage convergence
criteria, solver defaults, constitutive kernels, example inputs and historical
results are unchanged. Full nonlinear Q2 trajectories and accelerator checks
are outside this CPU elastic dispatch correction and were not run.