feat(solver): add diagnostic logging throughout solver pipeline
- solver.py: log solve entry (parts/constraints counts), system build
stats, convergence result with timing, decomposition decisions,
Newton/BFGS fallback events, and per-constraint diagnostics on failure
- solver.py: log drag lifecycle (pre_drag parts, drag_step timing/status,
post_drag step count summary)
- decompose.py: log cluster count, per-cluster body/constraint/residual
stats, and per-cluster convergence failures
- Init.py: add _FreeCADLogHandler routing Python logging.* calls to
FreeCAD.Console (PrintLog/PrintWarning/PrintError) with kindred_solver
logger at DEBUG level
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