docs(architecture): baseline current design

[jmagly]

Summary

• document the current T3MP3ST architecture and deployment topology
• record five architectural decisions and their consequences
• align vision, requirements, use cases, test strategy, and construction readiness
• preserve the completed intake and acceleration state for future iterations

Closes #108

Verification

• npx tsc --noEmit
• npm test (60 files, 644 tests; supplemental preflight and model-matrix suites green)
• npm run build
• markdownlint on all 27 changed Markdown files with MD013 disabled for prose/table line length (0 issues)
• jq empty .aiwg/working/sdlc-accelerate/state.json
• git diff --check

Risk and rollback

Documentation and AIWG planning artifacts only; no runtime behavior changes. Revert the merge commit to roll back.