docs: update all docs for sessions, solver, approvals, and recent features
- STATUS.md: migration count 18→23, endpoint count 86→~140, add approval
workflows, solver service, workstations, edit sessions, SSE targeted
delivery rows, update test file count 9→31, add migrations 019-023
- MODULES.md: add solver and sessions to registry, dependencies, endpoint
mappings (sections 3.11, 3.12), discovery response, admin settings,
config YAML, and future considerations
- CONFIGURATION.md: add Approval Workflows, Solver, and Modules config
sections, add SILO_SOLVER_DEFAULT env var
- ROADMAP.md: mark Job Queue Complete (Tier 0), Audit Trail Complete
(Tier 1), Approval/ECO Complete (Tier 4), update Workflow Engine tasks,
add Recently Completed section, update counts, resolve job queue question
- GAP_ANALYSIS.md: mark approval workflow Implemented, locking Partial,
update workflow comparison (C.2), update check-in/check-out to Partial,
task scheduler to Full, update endpoint counts, rewrite Appendix A
- INSTALL.md: add MODULES.md, WORKERS.md, SOLVER.md to Further Reading
- WORKERS.md: status Draft→Implemented
- SOLVER.md: add spec doc, mark Phase 3b as complete
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