D3: Documentation gaps (GDP solving guidance)

[bernalde]

Solving-GDP docs (doc/OnlineDocs/explanation/modeling/gdp/solving.rst, explanation/solvers/gdpopt.rst) don't cover:

• LD-SDA vs enumerate vs LOA/GLOA selection trade-offs (when is each appropriate);
• disjunctive bounds usage (once GDPopt: calc_disjunctive_bounds and obbt_disjunctive_bounds are accepted but silently ignored Pyomo/pyomo#4014 is resolved);
• exact_hull_quadratic caveats (NumPy requirement, mutable-Param freezing, PSD/NSD fallback behavior);
• single-tree MindtPy guidance beyond the current section (threads=1, persistent-solver requirements — cf. MindtPy: support single-tree LP/NLP B&B with APPSI / contrib.solver persistent interfaces Pyomo/pyomo#4020).

Docs-only; good first-contribution material for students.

Part of roadmap epic #2 (item D3).