Refactor/simplify codebase

[aviggiano]

• Use https://github.com/DietrichGebert/ponytail reviews and implement all suggestions
• Remove dead code
• Use https://github.com/mattpocock/skills such as improve-codebase-architecture and others that make sense
• To be done after ongoing work Prioritised work queue: publication fix, diagnostics blindness, smoke-lane causes, and reconciliation strategy #413

[aviggiano]

Closing this umbrella as not planned in its current form. The ponytail pass ran as #791/#812. Dead code was removed in #1174, #1175, #1178, #1181, #1193, #1197 and #1230. CI now blocks regressions with the knip exports/types/duplicates gate (#1219) and the global complexity ceiling (#1184, lowered to 83 in #1193). The remaining work has concrete trackers: #998 (artifact-gate hotspots), #1000 (monolithic runtime test files), #1232 (inert [execution] config), #1233, and #921 (sealed execution snapshots, which now also absorbs #1147). Once #921 narrows or retires sealing, it should also cover deduplicating the private isRecord/errorMessage copies that #812 deliberately left in the sealed/gate/authority and validator-identity modules.